diff --git a/backend/apps/app_factory.py b/backend/apps/app_factory.py
new file mode 100644
index 000000000..219da5b82
--- /dev/null
+++ b/backend/apps/app_factory.py
@@ -0,0 +1,108 @@
+"""
+FastAPI application factory with common configurations and exception handlers.
+"""
+import logging
+
+from fastapi import FastAPI, HTTPException
+from fastapi.middleware.cors import CORSMiddleware
+from fastapi.responses import JSONResponse
+
+from consts.exceptions import AppException
+
+
+logger = logging.getLogger(__name__)
+
+
+def create_app(
+    title: str = "Nexent API",
+    description: str = "",
+    version: str = "1.0.0",
+    root_path: str = "/api",
+    cors_origins: list = None,
+    cors_methods: list = None,
+    enable_monitoring: bool = True,
+) -> FastAPI:
+    """
+    Create a FastAPI application with common configurations.
+
+    Args:
+        title: API title
+        description: API description
+        version: API version
+        root_path: Root path for the API
+        cors_origins: List of allowed CORS origins (default: ["*"])
+        cors_methods: List of allowed CORS methods (default: ["*"])
+        enable_monitoring: Whether to enable monitoring
+
+    Returns:
+        Configured FastAPI application
+    """
+    app = FastAPI(
+        title=title,
+        description=description,
+        version=version,
+        root_path=root_path
+    )
+
+    # Add CORS middleware
+    app.add_middleware(
+        CORSMiddleware,
+        allow_origins=cors_origins or ["*"],
+        allow_credentials=True,
+        allow_methods=cors_methods or ["*"],
+        allow_headers=["*"],
+    )
+
+    # Register exception handlers
+    register_exception_handlers(app)
+
+    # Initialize monitoring if enabled
+    if enable_monitoring:
+        try:
+            from utils.monitoring import monitoring_manager
+            monitoring_manager.setup_fastapi_app(app)
+        except ImportError:
+            logger.warning("Monitoring utilities not available")
+
+    return app
+
+
+def register_exception_handlers(app: FastAPI) -> None:
+    """
+    Register common exception handlers for the FastAPI application.
+
+    Args:
+        app: FastAPI application instance
+    """
+
+    @app.exception_handler(HTTPException)
+    async def http_exception_handler(request, exc):
+        logger.error(f"HTTPException: {exc.detail}")
+        return JSONResponse(
+            status_code=exc.status_code,
+            content={"message": exc.detail},
+        )
+
+    @app.exception_handler(AppException)
+    async def app_exception_handler(request, exc):
+        logger.error(f"AppException: {exc.error_code.value} - {exc.message}")
+        return JSONResponse(
+            status_code=exc.http_status,
+            content={
+                "code": exc.error_code.value,
+                "message": exc.message,
+                "details": exc.details if exc.details else None
+            },
+        )
+
+    @app.exception_handler(Exception)
+    async def generic_exception_handler(request, exc):
+        # Don't catch AppException - it has its own handler
+        if isinstance(exc, AppException):
+            return await app_exception_handler(request, exc)
+
+        logger.error(f"Generic Exception: {exc}")
+        return JSONResponse(
+            status_code=500,
+            content={"message": "Internal server error, please try again later."},
+        )
diff --git a/backend/apps/config_app.py b/backend/apps/config_app.py
index 8691b15e0..fb6a0a4f0 100644
--- a/backend/apps/config_app.py
+++ b/backend/apps/config_app.py
@@ -1,9 +1,6 @@
 import logging
 
-from fastapi import FastAPI, HTTPException
-from fastapi.middleware.cors import CORSMiddleware
-from fastapi.responses import JSONResponse
-
+from apps.app_factory import create_app
 from apps.agent_app import agent_config_router as agent_router
 from apps.config_sync_app import router as config_sync_router
 from apps.datamate_app import router as datamate_router
@@ -26,21 +23,11 @@
 from apps.invitation_app import router as invitation_router
 from consts.const import IS_SPEED_MODE
 
-# Import monitoring utilities
-from utils.monitoring import monitoring_manager
-
 # Create logger instance
 logger = logging.getLogger("base_app")
-app = FastAPI(root_path="/api")
 
-# Add CORS middleware
-app.add_middleware(
-    CORSMiddleware,
-    allow_origins=["*"],  # Allows all origins
-    allow_credentials=True,
-    allow_methods=["*"],  # Allows all methods
-    allow_headers=["*"],  # Allows all headers
-)
+# Create FastAPI app with common configurations
+app = create_app(title="Nexent Config API", description="Configuration APIs")
 
 app.include_router(model_manager_router)
 app.include_router(config_sync_router)
@@ -69,26 +56,3 @@
 app.include_router(group_router)
 app.include_router(user_router)
 app.include_router(invitation_router)
-
-# Initialize monitoring for the application
-monitoring_manager.setup_fastapi_app(app)
-
-
-# Global exception handler for HTTP exceptions
-@app.exception_handler(HTTPException)
-async def http_exception_handler(request, exc):
-    logger.error(f"HTTPException: {exc.detail}")
-    return JSONResponse(
-        status_code=exc.status_code,
-        content={"message": exc.detail},
-    )
-
-
-# Global exception handler for all uncaught exceptions
-@app.exception_handler(Exception)
-async def generic_exception_handler(request, exc):
-    logger.error(f"Generic Exception: {exc}")
-    return JSONResponse(
-        status_code=500,
-        content={"message": "Internal server error, please try again later."},
-    )
diff --git a/backend/apps/dify_app.py b/backend/apps/dify_app.py
index c7d9321af..99ce8d86e 100644
--- a/backend/apps/dify_app.py
+++ b/backend/apps/dify_app.py
@@ -13,6 +13,8 @@
 from fastapi import APIRouter, Header, HTTPException, Query
 from fastapi.responses import JSONResponse
 
+from consts.error_code import ErrorCode
+from consts.exceptions import AppException
 from services.dify_service import fetch_dify_datasets_impl
 from utils.auth_utils import get_current_user_id
 
@@ -35,18 +37,10 @@ async def fetch_dify_datasets_api(
         # Normalize URL by removing trailing slash
         dify_api_base = dify_api_base.rstrip('/')
     except Exception as e:
-        raise HTTPException(
-            status_code=HTTPStatus.INTERNAL_SERVER_ERROR,
-            detail=f"Failed to fetch Dify datasets: {str(e)}"
-        )
+        logger.error(f"Invalid Dify configuration: {e}")
+        raise AppException(ErrorCode.DIFY_CONFIG_INVALID,
+                           f"Invalid URL format: {str(e)}")
 
-    try:
-        _, tenant_id = get_current_user_id(authorization)
-    except Exception as e:
-        raise HTTPException(
-            status_code=HTTPStatus.INTERNAL_SERVER_ERROR,
-            detail=f"Failed to fetch Dify datasets: {str(e)}"
-        )
 
     try:
         result = fetch_dify_datasets_impl(
@@ -57,15 +51,10 @@ async def fetch_dify_datasets_api(
             status_code=HTTPStatus.OK,
             content=result
         )
-    except ValueError as e:
-        logger.warning(f"Invalid Dify configuration: {e}")
-        raise HTTPException(
-            status_code=HTTPStatus.BAD_REQUEST,
-            detail=str(e)
-        )
+    except AppException:
+        # Re-raise AppException to be handled by global middleware
+        raise
     except Exception as e:
         logger.error(f"Failed to fetch Dify datasets: {e}")
-        raise HTTPException(
-            status_code=HTTPStatus.INTERNAL_SERVER_ERROR,
-            detail=f"Failed to fetch Dify datasets: {str(e)}"
-        )
+        raise AppException(ErrorCode.DIFY_SERVICE_ERROR,
+                           f"Failed to fetch Dify datasets: {str(e)}")
diff --git a/backend/apps/northbound_base_app.py b/backend/apps/northbound_base_app.py
index ff51e0e71..00e9f0462 100644
--- a/backend/apps/northbound_base_app.py
+++ b/backend/apps/northbound_base_app.py
@@ -1,47 +1,17 @@
-from http import HTTPStatus
 import logging
-from fastapi import FastAPI, HTTPException
-from fastapi.responses import JSONResponse
-from fastapi.middleware.cors import CORSMiddleware
 
+from apps.app_factory import create_app
 from .northbound_app import router as northbound_router
-from consts.exceptions import LimitExceededError, UnauthorizedError, SignatureValidationError
 
 logger = logging.getLogger("northbound_base_app")
 
-
-northbound_app = FastAPI(
+# Create FastAPI app with common configurations
+northbound_app = create_app(
     title="Nexent Northbound API",
     description="Northbound APIs for partners",
     version="1.0.0",
-    root_path="/api"
-)
-
-northbound_app.add_middleware(
-    CORSMiddleware,
-    allow_origins=["*"],
-    allow_credentials=True,
-    allow_methods=["GET", "POST", "PUT", "DELETE"],
-    allow_headers=["*"],
+    cors_methods=["GET", "POST", "PUT", "DELETE"],
+    enable_monitoring=False  # Disable monitoring for northbound API if not needed
 )
 
-
 northbound_app.include_router(northbound_router)
-
-
-@northbound_app.exception_handler(HTTPException)
-async def northbound_http_exception_handler(request, exc):
-    logger.error(f"Northbound HTTPException: {exc.detail}")
-    return JSONResponse(
-        status_code=exc.status_code,
-        content={"message": exc.detail},
-    )
-
-
-@northbound_app.exception_handler(Exception)
-async def northbound_generic_exception_handler(request, exc):
-    logger.error(f"Northbound Generic Exception: {exc}")
-    return JSONResponse(
-        status_code=HTTPStatus.INTERNAL_SERVER_ERROR,
-        content={"message": "Internal server error, please try again later."},
-    )
diff --git a/backend/apps/runtime_app.py b/backend/apps/runtime_app.py
index 6db480ab6..7420a14a2 100644
--- a/backend/apps/runtime_app.py
+++ b/backend/apps/runtime_app.py
@@ -1,58 +1,24 @@
 import logging
 
-from fastapi import FastAPI, HTTPException
-from fastapi.middleware.cors import CORSMiddleware
-from fastapi.responses import JSONResponse
-
+from apps.app_factory import create_app
 from apps.agent_app import agent_runtime_router as agent_router
 from apps.voice_app import voice_runtime_router as voice_router
 from apps.conversation_management_app import router as conversation_management_router
 from apps.memory_config_app import router as memory_config_router
 from apps.file_management_app import file_management_runtime_router as file_management_router
-
-# Import monitoring utilities
-from utils.monitoring import monitoring_manager
+from middleware.exception_handler import ExceptionHandlerMiddleware
 
 # Create logger instance
 logger = logging.getLogger("runtime_app")
-app = FastAPI(root_path="/api")
 
-# Add CORS middleware
-app.add_middleware(
-    CORSMiddleware,
-    allow_origins=["*"],
-    allow_credentials=True,
-    allow_methods=["*"],
-    allow_headers=["*"],
-)
+# Create FastAPI app with common configurations
+app = create_app(title="Nexent Runtime API", description="Runtime APIs")
+
+# Add global exception handler middleware
+app.add_middleware(ExceptionHandlerMiddleware)
 
 app.include_router(agent_router)
 app.include_router(conversation_management_router)
 app.include_router(memory_config_router)
 app.include_router(file_management_router)
 app.include_router(voice_router)
-
-# Initialize monitoring for the application
-monitoring_manager.setup_fastapi_app(app)
-
-
-# Global exception handler for HTTP exceptions
-@app.exception_handler(HTTPException)
-async def http_exception_handler(request, exc):
-    logger.error(f"HTTPException: {exc.detail}")
-    return JSONResponse(
-        status_code=exc.status_code,
-        content={"message": exc.detail},
-    )
-
-
-# Global exception handler for all uncaught exceptions
-@app.exception_handler(Exception)
-async def generic_exception_handler(request, exc):
-    logger.error(f"Generic Exception: {exc}")
-    return JSONResponse(
-        status_code=500,
-        content={"message": "Internal server error, please try again later."},
-    )
-
-
diff --git a/backend/consts/error_code.py b/backend/consts/error_code.py
new file mode 100644
index 000000000..73decbbf3
--- /dev/null
+++ b/backend/consts/error_code.py
@@ -0,0 +1,219 @@
+"""
+Error code definitions for the application.
+
+Format: XXYYZZ (6 digits, string)
+- XX: Module code (01-99, based on sidebar)
+    00: Common / 公共 - cross-module common errors
+    01: Chat / 开始问答
+    02: QuickConfig / 快速配置
+    03: AgentSpace / 智能体空间
+    04: AgentMarket / 智能体市场
+    05: AgentDev / 智能体开发
+    06: Knowledge / 知识库
+    07: MCPTools / MCP 工具
+    08: MonitorOps / 监控与运维
+    09: Model / 模型管理
+    10: Memory / 记忆管理
+    11: Profile / 个人信息
+    12: TenantResource / 租户资源
+    13: External / 外部服务 (DataMate, Dify)
+    15: Northbound / 北向接口
+    17: DataProcess / 数据处理
+    99: System / 系统级 - system internal errors
+- YY: Sub module category (01-99)
+- ZZ: Sequence in category (01-99)
+"""
+
+from enum import Enum
+
+
+class ErrorCode(Enum):
+    """Business error codes (stored as strings to preserve leading zeros)."""
+
+    # ==================== 00 Common / 公共 ====================
+    # 01 - Parameter & Validation
+    COMMON_VALIDATION_ERROR = "000101"  # Validation error
+    COMMON_PARAMETER_INVALID = "000102"  # Invalid parameter
+    COMMON_MISSING_REQUIRED_FIELD = "000103"  # Missing required field
+
+    # 02 - Auth & Permission
+    COMMON_UNAUTHORIZED = "000201"  # Not logged in / unauthenticated
+    COMMON_FORBIDDEN = "000202"  # No permission
+    COMMON_TOKEN_EXPIRED = "000203"  # Token expired
+    COMMON_TOKEN_INVALID = "000204"  # Invalid token
+
+    # 03 - External Service
+    COMMON_EXTERNAL_SERVICE_ERROR = "000301"  # External service error
+    COMMON_RATE_LIMIT_EXCEEDED = "000302"  # Rate limit exceeded
+
+    # 04 - File
+    FILE_NOT_FOUND = "000401"  # File not found
+    FILE_UPLOAD_FAILED = "000402"  # File upload failed
+    FILE_TOO_LARGE = "000403"  # File too large
+    FILE_TYPE_NOT_ALLOWED = "000404"  # File type not allowed
+    FILE_PREPROCESS_FAILED = "000405"  # File preprocess failed
+
+    # 05 - Resource
+    COMMON_RESOURCE_NOT_FOUND = "000501"  # Resource not found
+    COMMON_RESOURCE_ALREADY_EXISTS = "000502"  # Resource already exists
+    COMMON_RESOURCE_DISABLED = "000503"  # Resource disabled
+
+    # ==================== 01 Chat / 开始问答 ====================
+    # 01 - Conversation
+    CHAT_CONVERSATION_NOT_FOUND = "010101"  # Conversation not found
+    CHAT_MESSAGE_NOT_FOUND = "010102"  # Message not found
+    CHAT_CONVERSATION_SAVE_FAILED = "010103"  # Failed to save conversation
+    CHAT_TITLE_GENERATION_FAILED = "010104"  # Failed to generate title
+
+    # ==================== 02 QuickConfig / 快速配置 ====================
+    # 01 - Configuration
+    QUICK_CONFIG_INVALID = "020101"  # Invalid configuration
+    QUICK_CONFIG_SYNC_FAILED = "020102"  # Sync configuration failed
+
+    # ==================== 03 AgentSpace / 智能体空间 ====================
+    # 01 - Agent
+    AGENTSPACE_AGENT_NOT_FOUND = "030101"  # Agent not found
+    AGENTSPACE_AGENT_DISABLED = "030102"  # Agent disabled
+    AGENTSPACE_AGENT_RUN_FAILED = "030103"  # Agent run failed
+    AGENTSPACE_AGENT_NAME_DUPLICATE = "030104"  # Duplicate agent name
+    AGENTSPACE_VERSION_NOT_FOUND = "030105"  # Agent version not found
+
+    # ==================== 04 AgentMarket / 智能体市场 ====================
+    # 01 - Agent
+    AGENTMARKET_AGENT_NOT_FOUND = "040101"  # Agent not found in market
+
+    # ==================== 05 AgentDev / 智能体开发 ====================
+    # 01 - Configuration
+    AGENTDEV_CONFIG_INVALID = "050101"  # Invalid agent configuration
+    AGENTDEV_PROMPT_INVALID = "050102"  # Invalid prompt
+
+    # ==================== 06 Knowledge / 知识库 ====================
+    # 01 - Knowledge Base
+    KNOWLEDGE_NOT_FOUND = "060101"  # Knowledge not found
+    KNOWLEDGE_UPLOAD_FAILED = "060102"  # Upload failed
+    KNOWLEDGE_SYNC_FAILED = "060103"  # Sync failed
+    KNOWLEDGE_INDEX_NOT_FOUND = "060104"  # Index not found
+    KNOWLEDGE_SEARCH_FAILED = "060105"  # Search failed
+
+    # ==================== 07 MCPTools / MCP 工具 ====================
+    # 01 - Tool
+    MCP_TOOL_NOT_FOUND = "070101"  # Tool not found
+    MCP_TOOL_EXECUTION_FAILED = "070102"  # Tool execution failed
+    MCP_TOOL_CONFIG_INVALID = "070103"  # Invalid tool configuration
+
+    # 02 - Connection
+    MCP_CONNECTION_FAILED = "070201"  # MCP connection failed
+    MCP_CONTAINER_ERROR = "070202"  # MCP container error
+
+    # 03 - Configuration
+    MCP_NAME_ILLEGAL = "070301"  # Illegal MCP name
+
+    # ==================== 08 MonitorOps / 监控与运维 ====================
+    # 01 - Monitoring
+    MONITOROPS_METRIC_QUERY_FAILED = "080101"  # Metric query failed
+
+    # 02 - Alert
+    MONITOROPS_ALERT_CONFIG_INVALID = "080201"  # Invalid alert configuration
+
+    # ==================== 09 Model / 模型管理 ====================
+    # 01 - Model
+    MODEL_NOT_FOUND = "090101"  # Model not found
+    MODEL_CONFIG_INVALID = "090102"  # Invalid model configuration
+    MODEL_HEALTH_CHECK_FAILED = "090103"  # Health check failed
+    MODEL_PROVIDER_ERROR = "090104"  # Model provider error
+
+    # ==================== 10 Memory / 记忆管理 ====================
+    # 01 - Memory
+    MEMORY_NOT_FOUND = "100101"  # Memory not found
+    MEMORY_PREPARATION_FAILED = "100102"  # Memory preparation failed
+    MEMORY_CONFIG_INVALID = "100103"  # Invalid memory configuration
+
+    # ==================== 11 Profile / 个人信息 ====================
+    # 01 - User
+    PROFILE_USER_NOT_FOUND = "110101"  # User not found
+    PROFILE_UPDATE_FAILED = "110102"  # Profile update failed
+    PROFILE_USER_ALREADY_EXISTS = "110103"  # User already exists
+    PROFILE_INVALID_CREDENTIALS = "110104"  # Invalid credentials
+
+    # ==================== 12 TenantResource / 租户资源 ====================
+    # 01 - Tenant
+    TENANT_NOT_FOUND = "120101"  # Tenant not found
+    TENANT_DISABLED = "120102"  # Tenant disabled
+    TENANT_CONFIG_ERROR = "120103"  # Tenant configuration error
+    TENANT_RESOURCE_EXCEEDED = "120104"  # Tenant resource exceeded
+
+    # ==================== 13 External / 外部服务 ====================
+    # 01 - DataMate
+    DATAMATE_CONNECTION_FAILED = "130101"  # DataMate connection failed
+
+    # 02 - Dify
+    DIFY_SERVICE_ERROR = "130201"  # Dify service error
+    DIFY_CONFIG_INVALID = "130202"  # Invalid Dify configuration
+    DIFY_CONNECTION_ERROR = "130203"  # Dify connection error
+    DIFY_AUTH_ERROR = "130204"  # Dify auth error
+    DIFY_RATE_LIMIT = "130205"  # Dify rate limit
+    DIFY_RESPONSE_ERROR = "130206"  # Dify response error
+
+    # 03 - ME Service
+    ME_CONNECTION_FAILED = "130301"  # ME service connection failed
+
+    # ==================== 14 Northbound / 北向接口 ====================
+    # 01 - Request
+    NORTHBOUND_REQUEST_FAILED = "140101"  # Northbound request failed
+
+    # 02 - Configuration
+    NORTHBOUND_CONFIG_INVALID = "140201"  # Invalid northbound configuration
+
+    # ==================== 15 DataProcess / 数据处理 ====================
+    # 01 - Task
+    DATAPROCESS_TASK_FAILED = "150101"  # Data process task failed
+    DATAPROCESS_PARSE_FAILED = "150102"  # Data parse failed
+
+    # ==================== 99 System / 系统级 ====================
+    # 01 - System Errors
+    SYSTEM_UNKNOWN_ERROR = "990101"  # Unknown error
+    SYSTEM_SERVICE_UNAVAILABLE = "990102"  # Service unavailable
+    SYSTEM_DATABASE_ERROR = "990103"  # Database error
+    SYSTEM_TIMEOUT = "990104"  # Timeout
+    SYSTEM_INTERNAL_ERROR = "990105"  # Internal error
+
+    # 02 - Config
+    CONFIG_NOT_FOUND = "990201"  # Configuration not found
+    CONFIG_UPDATE_FAILED = "990202"  # Configuration update failed
+
+
+# HTTP status code mapping
+ERROR_CODE_HTTP_STATUS = {
+    # Common - Auth
+    ErrorCode.COMMON_UNAUTHORIZED: 401,
+    ErrorCode.COMMON_TOKEN_EXPIRED: 401,
+    ErrorCode.COMMON_TOKEN_INVALID: 401,
+    ErrorCode.COMMON_FORBIDDEN: 403,
+    # Common - Validation
+    ErrorCode.COMMON_VALIDATION_ERROR: 400,
+    ErrorCode.COMMON_PARAMETER_INVALID: 400,
+    ErrorCode.COMMON_MISSING_REQUIRED_FIELD: 400,
+    # Common - Rate Limit
+    ErrorCode.COMMON_RATE_LIMIT_EXCEEDED: 429,
+    # Common - Resource
+    ErrorCode.COMMON_RESOURCE_NOT_FOUND: 404,
+    ErrorCode.COMMON_RESOURCE_ALREADY_EXISTS: 409,
+    ErrorCode.COMMON_RESOURCE_DISABLED: 403,
+    # Common - File
+    ErrorCode.FILE_NOT_FOUND: 404,
+    ErrorCode.FILE_UPLOAD_FAILED: 500,
+    ErrorCode.FILE_TOO_LARGE: 413,
+    ErrorCode.FILE_TYPE_NOT_ALLOWED: 400,
+    ErrorCode.FILE_PREPROCESS_FAILED: 500,
+    # System
+    ErrorCode.SYSTEM_SERVICE_UNAVAILABLE: 503,
+    ErrorCode.SYSTEM_TIMEOUT: 504,
+    ErrorCode.SYSTEM_DATABASE_ERROR: 500,
+    ErrorCode.SYSTEM_INTERNAL_ERROR: 500,
+    # Dify (module 13)
+    ErrorCode.DIFY_CONFIG_INVALID: 400,
+    ErrorCode.DIFY_AUTH_ERROR: 401,
+    ErrorCode.DIFY_CONNECTION_ERROR: 502,
+    ErrorCode.DIFY_RESPONSE_ERROR: 502,
+    ErrorCode.DIFY_RATE_LIMIT: 429,
+}
diff --git a/backend/consts/error_message.py b/backend/consts/error_message.py
new file mode 100644
index 000000000..aa7bf45e3
--- /dev/null
+++ b/backend/consts/error_message.py
@@ -0,0 +1,148 @@
+"""
+Error message mappings for error codes.
+
+This module provides default English error messages.
+Frontend should use i18n for localized messages.
+"""
+
+from .error_code import ErrorCode
+
+
+class ErrorMessage:
+    """Error code to message mapping."""
+
+    _MESSAGES = {
+        # ==================== 00 Common / 公共 ====================
+        # 00 - Parameter & Validation
+        ErrorCode.COMMON_VALIDATION_ERROR: "Validation failed.",
+        ErrorCode.COMMON_PARAMETER_INVALID: "Invalid parameter.",
+        ErrorCode.COMMON_MISSING_REQUIRED_FIELD: "Required field is missing.",
+        # 01 - Auth & Permission
+        ErrorCode.COMMON_UNAUTHORIZED: "You are not authorized to perform this action.",
+        ErrorCode.COMMON_FORBIDDEN: "Access forbidden.",
+        ErrorCode.COMMON_TOKEN_EXPIRED: "Your session has expired. Please login again.",
+        ErrorCode.COMMON_TOKEN_INVALID: "Invalid token. Please login again.",
+        # 02 - External Service
+        ErrorCode.COMMON_EXTERNAL_SERVICE_ERROR: "External service error.",
+        ErrorCode.COMMON_RATE_LIMIT_EXCEEDED: "Too many requests. Please try again later.",
+        # 03 - File
+        ErrorCode.FILE_NOT_FOUND: "File not found.",
+        ErrorCode.FILE_UPLOAD_FAILED: "Failed to upload file.",
+        ErrorCode.FILE_TOO_LARGE: "File size exceeds limit.",
+        ErrorCode.FILE_TYPE_NOT_ALLOWED: "File type not allowed.",
+        ErrorCode.FILE_PREPROCESS_FAILED: "File preprocessing failed.",
+        # 04 - Resource
+        ErrorCode.COMMON_RESOURCE_NOT_FOUND: "Resource not found.",
+        ErrorCode.COMMON_RESOURCE_ALREADY_EXISTS: "Resource already exists.",
+        ErrorCode.COMMON_RESOURCE_DISABLED: "Resource is disabled.",
+
+        # ==================== 01 Chat / 开始问答 ====================
+        ErrorCode.CHAT_CONVERSATION_NOT_FOUND: "Conversation not found.",
+        ErrorCode.CHAT_MESSAGE_NOT_FOUND: "Message not found.",
+        ErrorCode.CHAT_CONVERSATION_SAVE_FAILED: "Failed to save conversation.",
+        ErrorCode.CHAT_TITLE_GENERATION_FAILED: "Failed to generate conversation title.",
+
+        # ==================== 02 QuickConfig / 快速配置 ====================
+        ErrorCode.QUICK_CONFIG_INVALID: "Invalid configuration.",
+        ErrorCode.QUICK_CONFIG_SYNC_FAILED: "Sync configuration failed.",
+
+        # ==================== 03 AgentSpace / 智能体空间 ====================
+        ErrorCode.AGENTSPACE_AGENT_NOT_FOUND: "Agent not found.",
+        ErrorCode.AGENTSPACE_AGENT_DISABLED: "Agent is disabled.",
+        ErrorCode.AGENTSPACE_AGENT_RUN_FAILED: "Failed to run agent. Please try again later.",
+        ErrorCode.AGENTSPACE_AGENT_NAME_DUPLICATE: "Agent name already exists.",
+        ErrorCode.AGENTSPACE_VERSION_NOT_FOUND: "Agent version not found.",
+
+        # ==================== 04 AgentMarket / 智能体市场 ====================
+        ErrorCode.AGENTMARKET_AGENT_NOT_FOUND: "Agent not found in market.",
+
+        # ==================== 05 AgentDev / 智能体开发 ====================
+        ErrorCode.AGENTDEV_CONFIG_INVALID: "Invalid agent configuration.",
+        ErrorCode.AGENTDEV_PROMPT_INVALID: "Invalid prompt.",
+
+        # ==================== 06 Knowledge / 知识库 ====================
+        ErrorCode.KNOWLEDGE_NOT_FOUND: "Knowledge base not found.",
+        ErrorCode.KNOWLEDGE_UPLOAD_FAILED: "Failed to upload knowledge.",
+        ErrorCode.KNOWLEDGE_SYNC_FAILED: "Failed to sync knowledge base.",
+        ErrorCode.KNOWLEDGE_INDEX_NOT_FOUND: "Search index not found.",
+        ErrorCode.KNOWLEDGE_SEARCH_FAILED: "Knowledge search failed.",
+
+        # ==================== 07 MCPTools / MCP 工具 ====================
+        ErrorCode.MCP_TOOL_NOT_FOUND: "Tool not found.",
+        ErrorCode.MCP_TOOL_EXECUTION_FAILED: "Tool execution failed.",
+        ErrorCode.MCP_TOOL_CONFIG_INVALID: "Tool configuration is invalid.",
+        ErrorCode.MCP_CONNECTION_FAILED: "Failed to connect to MCP service.",
+        ErrorCode.MCP_CONTAINER_ERROR: "MCP container operation failed.",
+        ErrorCode.MCP_NAME_ILLEGAL: "MCP name contains invalid characters.",
+
+        # ==================== 08 MonitorOps / 监控与运维 ====================
+        ErrorCode.MONITOROPS_METRIC_QUERY_FAILED: "Metric query failed.",
+        ErrorCode.MONITOROPS_ALERT_CONFIG_INVALID: "Invalid alert configuration.",
+
+        # ==================== 09 Model / 模型管理 ====================
+        ErrorCode.MODEL_NOT_FOUND: "Model not found.",
+        ErrorCode.MODEL_CONFIG_INVALID: "Model configuration is invalid.",
+        ErrorCode.MODEL_HEALTH_CHECK_FAILED: "Model health check failed.",
+        ErrorCode.MODEL_PROVIDER_ERROR: "Model provider error.",
+
+        # ==================== 10 Memory / 记忆管理 ====================
+        ErrorCode.MEMORY_NOT_FOUND: "Memory not found.",
+        ErrorCode.MEMORY_PREPARATION_FAILED: "Failed to prepare memory.",
+        ErrorCode.MEMORY_CONFIG_INVALID: "Memory configuration is invalid.",
+
+        # ==================== 11 Profile / 个人信息 ====================
+        ErrorCode.PROFILE_USER_NOT_FOUND: "User not found.",
+        ErrorCode.PROFILE_UPDATE_FAILED: "Profile update failed.",
+        ErrorCode.PROFILE_USER_ALREADY_EXISTS: "User already exists.",
+        ErrorCode.PROFILE_INVALID_CREDENTIALS: "Invalid username or password.",
+
+        # ==================== 12 TenantResource / 租户资源 ====================
+        ErrorCode.TENANT_NOT_FOUND: "Tenant not found.",
+        ErrorCode.TENANT_DISABLED: "Tenant is disabled.",
+        ErrorCode.TENANT_CONFIG_ERROR: "Tenant configuration error.",
+        ErrorCode.TENANT_RESOURCE_EXCEEDED: "Tenant resource exceeded.",
+
+        # ==================== 13 External / 外部服务 ====================
+        ErrorCode.DATAMATE_CONNECTION_FAILED: "Failed to connect to DataMate service.",
+        ErrorCode.DIFY_SERVICE_ERROR: "Dify service error.",
+        ErrorCode.DIFY_CONFIG_INVALID: "Dify configuration invalid. Please check URL and API key format.",
+        ErrorCode.DIFY_CONNECTION_ERROR: "Failed to connect to Dify. Please check network connection and URL.",
+        ErrorCode.DIFY_RESPONSE_ERROR: "Failed to parse Dify response. Please check API URL.",
+        ErrorCode.DIFY_AUTH_ERROR: "Dify authentication failed. Please check your API key.",
+        ErrorCode.DIFY_RATE_LIMIT: "Dify API rate limit exceeded. Please try again later.",
+        ErrorCode.ME_CONNECTION_FAILED: "Failed to connect to ME service.",
+
+        # ==================== 14 Northbound / 北向接口 ====================
+        ErrorCode.NORTHBOUND_REQUEST_FAILED: "Northbound request failed.",
+        ErrorCode.NORTHBOUND_CONFIG_INVALID: "Invalid northbound configuration.",
+
+        # ==================== 15 DataProcess / 数据处理 ====================
+        ErrorCode.DATAPROCESS_TASK_FAILED: "Data process task failed.",
+        ErrorCode.DATAPROCESS_PARSE_FAILED: "Data parsing failed.",
+
+        # ==================== 99 System / 系统级 ====================
+        # 01 - System Errors
+        ErrorCode.SYSTEM_UNKNOWN_ERROR: "An unknown error occurred. Please try again later.",
+        ErrorCode.SYSTEM_SERVICE_UNAVAILABLE: "Service is temporarily unavailable. Please try again later.",
+        ErrorCode.SYSTEM_DATABASE_ERROR: "Database operation failed. Please try again later.",
+        ErrorCode.SYSTEM_TIMEOUT: "Operation timed out. Please try again later.",
+        ErrorCode.SYSTEM_INTERNAL_ERROR: "Internal server error. Please try again later.",
+        # 02 - Config
+        ErrorCode.CONFIG_NOT_FOUND: "Configuration not found.",
+        ErrorCode.CONFIG_UPDATE_FAILED: "Configuration update failed.",
+    }
+
+    @classmethod
+    def get_message(cls, error_code: ErrorCode) -> str:
+        """Get error message by error code."""
+        return cls._MESSAGES.get(error_code, "An error occurred. Please try again later.")
+
+    @classmethod
+    def get_message_with_code(cls, error_code: ErrorCode) -> tuple[int, str]:
+        """Get error code and message as tuple."""
+        return (error_code.value, cls.get_message(error_code))
+
+    @classmethod
+    def get_all_messages(cls) -> dict:
+        """Get all error code to message mappings."""
+        return {code.value: msg for code, msg in cls._MESSAGES.items()}
diff --git a/backend/consts/exceptions.py b/backend/consts/exceptions.py
index 94b1f770d..e9d270673 100644
--- a/backend/consts/exceptions.py
+++ b/backend/consts/exceptions.py
@@ -1,7 +1,74 @@
 """
 Custom exception classes for the application.
+
+This module provides two types of exceptions:
+
+1. New Framework (with ErrorCode):
+   from consts.error_code import ErrorCode
+   from consts.exceptions import AppException
+   
+   raise AppException(ErrorCode.COMMON_VALIDATION_ERROR, "Validation failed")
+   raise AppException(ErrorCode.MCP_CONNECTION_FAILED, "Connection timeout", details={"host": "localhost"})
+
+2. Legacy Framework (simple exceptions):
+   from consts.exceptions import ValidationError, NotFoundException, MCPConnectionError
+   
+   raise ValidationError("Tenant name cannot be empty")
+   raise NotFoundException("Tenant 123 not found")
+   raise MCPConnectionError("MCP connection failed")
+
+The exception handler automatically maps legacy exception class names to ErrorCode.
 """
 
+from .error_code import ErrorCode, ERROR_CODE_HTTP_STATUS
+from .error_message import ErrorMessage
+
+
+# ==================== New Framework: AppException with ErrorCode ====================
+
+class AppException(Exception):
+    """
+    Base application exception with ErrorCode.
+
+    Usage:
+        raise AppException(ErrorCode.COMMON_VALIDATION_ERROR, "Validation failed")
+        raise AppException(ErrorCode.MCP_CONNECTION_FAILED, "Timeout", details={"host": "x"})
+    """
+
+    def __init__(self, error_code: ErrorCode, message: str = None, details: dict = None):
+        self.error_code = error_code
+        self.message = message or ErrorMessage.get_message(error_code)
+        self.details = details or {}
+        super().__init__(self.message)
+
+    def to_dict(self) -> dict:
+        return {
+            "code": int(self.error_code.value),
+            "message": self.message,
+            "details": self.details if self.details else None
+        }
+
+    @property
+    def http_status(self) -> int:
+        return ERROR_CODE_HTTP_STATUS.get(self.error_code, 500)
+
+
+def raise_error(error_code: ErrorCode, message: str = None, details: dict = None):
+    """Raise an AppException with the given error code."""
+    raise AppException(error_code, message, details)
+
+
+# ==================== Legacy Framework: Simple Exception Classes ====================
+# These are simple exceptions that work with the old calling pattern.
+# The exception handler automatically maps class names to ErrorCode.
+#
+# Usage (unchanged from before):
+#     raise ValidationError("Invalid input")
+#     raise NotFoundException("Resource not found")
+#     raise MCPConnectionError("Connection failed")
+#
+# These do NOT require ErrorCode - they are simple Exception subclasses.
+# Exception handler will infer ErrorCode from class name.
 
 class AgentRunException(Exception):
     """Exception raised when agent run fails."""
@@ -58,7 +125,6 @@ class TimeoutException(Exception):
     pass
 
 
-
 class ValidationError(Exception):
     """Raised when validation fails."""
     pass
@@ -70,7 +136,7 @@ class NotFoundException(Exception):
 
 
 class MEConnectionException(Exception):
-    """Raised when not found exception occurs."""
+    """Raised when ME connection fails."""
     pass
 
 
@@ -112,3 +178,48 @@ class DuplicateError(Exception):
 class DataMateConnectionError(Exception):
     """Raised when DataMate connection fails or URL is not configured."""
     pass
+
+
+# ==================== Legacy Aliases (same as above, for compatibility) ====================
+# These are additional aliases that map to the same simple exception classes above.
+# They provide backward compatibility for code that uses these names.
+
+# Common aliases
+ParameterInvalidError = ValidationError
+ForbiddenError = Exception  # Generic fallback
+ServiceUnavailableError = Exception  # Generic fallback
+DatabaseError = Exception  # Generic fallback
+TimeoutError = TimeoutException
+UnknownError = Exception  # Generic fallback
+
+# Domain specific aliases
+UserNotFoundError = NotFoundException
+UserAlreadyExistsError = DuplicateError
+InvalidCredentialsError = UnauthorizedError
+
+TenantNotFoundError = NotFoundException
+TenantDisabledError = Exception  # Generic fallback
+
+AgentNotFoundError = NotFoundException
+AgentDisabledError = Exception  # Generic fallback
+
+ToolNotFoundError = NotFoundException
+
+ConversationNotFoundError = NotFoundException
+
+MemoryNotFoundError = NotFoundException
+KnowledgeNotFoundError = NotFoundException
+
+ModelNotFoundError = NotFoundException
+
+# File aliases
+FileNotFoundError = NotFoundException
+FileUploadFailedError = Exception  # Generic fallback
+FileTooLargeError = Exception  # Generic fallback
+
+# External service aliases
+DifyServiceException = Exception  # Generic fallback
+ExternalAPIError = Exception  # Generic fallback
+
+# Signature aliases
+# SignatureValidationError already defined above
diff --git a/backend/middleware/__init__.py b/backend/middleware/__init__.py
new file mode 100644
index 000000000..937f10972
--- /dev/null
+++ b/backend/middleware/__init__.py
@@ -0,0 +1 @@
+# Backend middleware package
diff --git a/backend/middleware/exception_handler.py b/backend/middleware/exception_handler.py
new file mode 100644
index 000000000..14d9ebb38
--- /dev/null
+++ b/backend/middleware/exception_handler.py
@@ -0,0 +1,176 @@
+"""
+Global exception handler middleware.
+
+This middleware provides centralized error handling for the FastAPI application.
+It catches all exceptions and returns a standardized JSON response.
+"""
+
+import logging
+import traceback
+import uuid
+from typing import Callable
+
+from fastapi import Request, Response, HTTPException
+from fastapi.responses import JSONResponse
+from starlette.middleware.base import BaseHTTPMiddleware
+
+from consts.error_code import ErrorCode, ERROR_CODE_HTTP_STATUS
+from consts.error_message import ErrorMessage
+
+logger = logging.getLogger(__name__)
+
+
+def _http_status_to_error_code(status_code: int) -> ErrorCode:
+    """Map HTTP status codes to internal error codes for backward compatibility."""
+    mapping = {
+        400: ErrorCode.COMMON_VALIDATION_ERROR,
+        401: ErrorCode.COMMON_UNAUTHORIZED,
+        403: ErrorCode.COMMON_FORBIDDEN,
+        404: ErrorCode.COMMON_RESOURCE_NOT_FOUND,
+        429: ErrorCode.COMMON_RATE_LIMIT_EXCEEDED,
+        500: ErrorCode.SYSTEM_INTERNAL_ERROR,
+        502: ErrorCode.SYSTEM_SERVICE_UNAVAILABLE,
+        503: ErrorCode.SYSTEM_SERVICE_UNAVAILABLE,
+    }
+    return mapping.get(status_code, ErrorCode.SYSTEM_UNKNOWN_ERROR)
+
+
+class ExceptionHandlerMiddleware(BaseHTTPMiddleware):
+    """
+    Global exception handler middleware.
+
+    This middleware catches all exceptions and returns a standardized response:
+    - For AppException: returns the error code and message
+    - For other exceptions: logs the error and returns a generic error response
+    """
+
+    async def dispatch(self, request: Request, call_next: Callable) -> Response:
+        # Generate trace ID for request tracking
+        trace_id = str(uuid.uuid4())
+        request.state.trace_id = trace_id
+
+        try:
+            response = await call_next(request)
+            return response
+        except Exception as exc:
+            # Check if it's an AppException by looking for the error_code attribute
+            # This handles both import path variations (backend.consts.exceptions vs consts.exceptions)
+            if hasattr(exc, 'error_code'):
+                # This is an AppException - get http_status from mapping
+                logger.error(
+                    f"[{trace_id}] AppException: {exc.error_code.value} - {exc.message}",
+                    extra={"trace_id": trace_id,
+                           "error_code": exc.error_code.value}
+                )
+
+                # Use HTTP status from error code mapping, default to 500
+                # Try to get http_status property first, then fall back to ERROR_CODE_HTTP_STATUS mapping
+                if hasattr(exc, 'http_status'):
+                    http_status = exc.http_status
+                else:
+                    http_status = ERROR_CODE_HTTP_STATUS.get(
+                        exc.error_code, 500)
+
+                return JSONResponse(
+                    status_code=http_status,
+                    content={
+                        "code": int(exc.error_code.value),
+                        "message": exc.message,
+                        "trace_id": trace_id,
+                        "details": exc.details if exc.details else None
+                    }
+                )
+            elif isinstance(exc, HTTPException):
+                # Handle FastAPI HTTPException for backward compatibility
+                # Map HTTP status codes to error codes
+                error_code = _http_status_to_error_code(exc.status_code)
+
+                return JSONResponse(
+                    status_code=exc.status_code,
+                    content={
+                        "code": int(error_code.value),
+                        "message": exc.detail,
+                        "trace_id": trace_id
+                    }
+                )
+            else:
+                # Log the full exception with traceback
+                logger.error(
+                    f"[{trace_id}] Unhandled exception: {str(exc)}",
+                    exc_info=True,
+                    extra={"trace_id": trace_id}
+                )
+
+                # Return generic error response with proper HTTP 500 status
+                # Using mixed mode: HTTP status code + business error code
+                return JSONResponse(
+                    status_code=500,
+                    content={
+                        "code": ErrorCode.SYSTEM_INTERNAL_ERROR.value,
+                        "message": ErrorMessage.get_message(ErrorCode.SYSTEM_INTERNAL_ERROR),
+                        "trace_id": trace_id,
+                        "details": None
+                    }
+                )
+
+
+def create_error_response(
+    error_code: ErrorCode,
+    message: str = None,
+    trace_id: str = None,
+    details: dict = None,
+    http_status: int = None
+) -> JSONResponse:
+    """
+    Create a standardized error response with mixed mode (HTTP status + business error code).
+
+    Args:
+        error_code: The error code
+        message: Optional custom message (defaults to standard message)
+        trace_id: Optional trace ID for tracking
+        details: Optional additional details
+        http_status: Optional HTTP status code (defaults to mapping from error_code)
+
+    Returns:
+        JSONResponse with standardized error format
+    """
+    # Use provided http_status or get from error code mapping
+    status = http_status if http_status else ERROR_CODE_HTTP_STATUS.get(
+        error_code, 500)
+
+    return JSONResponse(
+        status_code=status,
+        content={
+            "code": int(error_code.value),
+            "message": message or ErrorMessage.get_message(error_code),
+            "trace_id": trace_id,
+            "details": details
+        }
+    )
+
+
+def create_success_response(
+    data: any = None,
+    message: str = "OK",
+    trace_id: str = None
+) -> JSONResponse:
+    """
+    Create a standardized success response.
+
+    Args:
+        data: The response data
+        message: Optional success message
+        trace_id: Optional trace ID for tracking
+
+    Returns:
+        JSONResponse with standardized success format
+    """
+    return JSONResponse(
+        status_code=200,
+        content={
+            "code": 0,  # 0 indicates success
+            "message": message,
+            "data": data,
+            "trace_id": trace_id
+        }
+    )
diff --git a/backend/services/dify_service.py b/backend/services/dify_service.py
index 14e3a4d6f..76c297292 100644
--- a/backend/services/dify_service.py
+++ b/backend/services/dify_service.py
@@ -12,6 +12,8 @@
 
 import httpx
 
+from consts.error_code import ErrorCode
+from consts.exceptions import AppException
 from nexent.utils.http_client_manager import http_client_manager
 
 logger = logging.getLogger("dify_service")
@@ -67,11 +69,21 @@ def fetch_dify_datasets_impl(
     """
     # Validate inputs
     if not dify_api_base or not isinstance(dify_api_base, str):
-        raise ValueError(
-            "dify_api_base is required and must be a non-empty string")
+        raise AppException(
+            ErrorCode.DIFY_CONFIG_INVALID,
+            "Dify API URL is required and must be a non-empty string"
+        )
+
+    # Validate URL format
+    if not (dify_api_base.startswith("http://") or dify_api_base.startswith("https://")):
+        raise AppException(
+            ErrorCode.DIFY_CONFIG_INVALID,
+            "Dify API URL must start with http:// or https://"
+        )
 
     if not api_key or not isinstance(api_key, str):
-        raise ValueError("api_key is required and must be a non-empty string")
+        raise AppException(ErrorCode.DIFY_CONFIG_INVALID,
+                           "Dify API key is required and must be a non-empty string")
 
     # Normalize API base URL
     api_base = dify_api_base.rstrip("/")
@@ -95,7 +107,7 @@ def fetch_dify_datasets_impl(
         # Use shared HttpClientManager for connection pooling
         client = http_client_manager.get_sync_client(
             base_url=api_base,
-            timeout=30.0,
+            timeout=10.0,
             verify_ssl=False
         )
         response = client.get(url, headers=headers)
@@ -157,15 +169,35 @@ def fetch_dify_datasets_impl(
 
     except httpx.RequestError as e:
         logger.error(f"Dify API request failed: {str(e)}")
-        raise Exception(f"Dify API request failed: {str(e)}")
+        raise AppException(ErrorCode.DIFY_CONNECTION_ERROR,
+                           f"Dify API request failed: {str(e)}")
     except httpx.HTTPStatusError as e:
-        logger.error(f"Dify API HTTP error: {str(e)}")
-        raise Exception(f"Dify API HTTP error: {str(e)}")
+        logger.error(
+            f"Dify API HTTP error: {str(e)}, status_code: {e.response.status_code}")
+        # Map HTTP status to specific error code
+        if e.response.status_code == 401:
+            logger.error("Raising DIFY_AUTH_ERROR for 401 error")
+            raise AppException(ErrorCode.DIFY_AUTH_ERROR,
+                               f"Dify authentication failed: {str(e)}")
+        elif e.response.status_code == 403:
+            logger.error("Raising DIFY_AUTH_ERROR for 403 error")
+            raise AppException(ErrorCode.DIFY_AUTH_ERROR,
+                               f"Dify access forbidden: {str(e)}")
+        elif e.response.status_code == 429:
+            logger.error("Raising DIFY_RATE_LIMIT for 429 error")
+            raise AppException(ErrorCode.DIFY_RATE_LIMIT,
+                               f"Dify API rate limit exceeded: {str(e)}")
+        else:
+            logger.error(
+                f"Raising DIFY_SERVICE_ERROR for status {e.response.status_code}")
+            raise AppException(ErrorCode.DIFY_SERVICE_ERROR,
+                               f"Dify API HTTP error {e.response.status_code}: {str(e)}")
     except json.JSONDecodeError as e:
         logger.error(f"Failed to parse Dify API response: {str(e)}")
-        raise Exception(f"Failed to parse Dify API response: {str(e)}")
+        raise AppException(ErrorCode.DIFY_RESPONSE_ERROR,
+                           f"Failed to parse Dify API response: {str(e)}")
     except KeyError as e:
         logger.error(
             f"Unexpected Dify API response format: missing key {str(e)}")
-        raise Exception(
-            f"Unexpected Dify API response format: missing key {str(e)}")
+        raise AppException(ErrorCode.DIFY_RESPONSE_ERROR,
+                           f"Unexpected Dify API response format: missing key {str(e)}")
diff --git a/frontend/const/errorCode.ts b/frontend/const/errorCode.ts
new file mode 100644
index 000000000..88b8ba0cb
--- /dev/null
+++ b/frontend/const/errorCode.ts
@@ -0,0 +1,207 @@
+/**
+ * Error code definitions for the frontend.
+ *
+ * Format: XXYYZZ (6 digits string) - Must match backend/consts/error_code.py
+ * - XX: Module code (01-99)
+ * - YY: Sub module category (01-99)
+ * - ZZ: Sequence in category (01-99)
+ *
+ * Module Numbers:
+ * - 00: Common / 公共
+ * - 01: Chat / 开始问答
+ * - 02: QuickConfig / 快速配置
+ * - 03: AgentSpace / 智能体空间
+ * - 04: AgentMarket / 智能体市场
+ * - 05: AgentDev / 智能体开发
+ * - 06: Knowledge / 知识库
+ * - 07: MCPTools / MCP 工具
+ * - 08: MonitorOps / 监控与运维
+ * - 09: Model / 模型管理
+ * - 10: Memory / 记忆管理
+ * - 11: Profile / 个人信息
+ * - 12: TenantResource / 租户资源
+ * - 13: External / 外部服务
+ * - 14: Northbound / 北向接口
+ * - 15: DataProcess / 数据处理
+ * - 99: System / 系统级
+ */
+
+export const ErrorCode = {
+  // ==================== 00 Common / 公共 ====================
+  // 01 - Parameter & Validation
+  VALIDATION_ERROR: "000101",
+  PARAMETER_INVALID: "000102",
+  MISSING_REQUIRED_FIELD: "000103",
+
+  // 02 - Auth & Permission
+  UNAUTHORIZED: "000201",
+  FORBIDDEN: "000202",
+  TOKEN_EXPIRED: "000203",
+  TOKEN_INVALID: "000204",
+
+  // 03 - External Service
+  EXTERNAL_SERVICE_ERROR: "000301",
+  RATE_LIMIT_EXCEEDED: "000302",
+
+  // 04 - File
+  FILE_NOT_FOUND: "000401",
+  FILE_UPLOAD_FAILED: "000402",
+  FILE_TOO_LARGE: "000403",
+  FILE_TYPE_NOT_ALLOWED: "000404",
+  FILE_PREPROCESS_FAILED: "000405",
+
+  // 05 - Resource
+  RESOURCE_NOT_FOUND: "000501",
+  RESOURCE_ALREADY_EXISTS: "000502",
+  RESOURCE_DISABLED: "000503",
+
+  // ==================== 01 Chat / 开始问答 ====================
+  // 01 - Conversation
+  CONVERSATION_NOT_FOUND: "010101",
+  MESSAGE_NOT_FOUND: "010102",
+  CONVERSATION_SAVE_FAILED: "010103",
+  CONVERSATION_TITLE_GENERATION_FAILED: "010104",
+
+  // ==================== 02 QuickConfig / 快速配置 ====================
+  // 01 - Configuration
+  QUICK_CONFIG_INVALID: "020101",
+  QUICK_CONFIG_SYNC_FAILED: "020102",
+
+  // ==================== 03 AgentSpace / 智能体空间 ====================
+  // 01 - Agent
+  AGENT_NOT_FOUND: "030101",
+  AGENT_DISABLED: "030102",
+  AGENT_RUN_FAILED: "030103",
+  AGENT_NAME_DUPLICATE: "030104",
+  AGENT_VERSION_NOT_FOUND: "030105",
+
+  // ==================== 04 AgentMarket / 智能体市场 ====================
+  // 01 - Agent
+  AGENTMARKET_AGENT_NOT_FOUND: "040101",
+
+  // ==================== 05 AgentDev / 智能体开发 ====================
+  // 01 - Configuration
+  AGENTDEV_CONFIG_INVALID: "050101",
+  AGENTDEV_PROMPT_INVALID: "050102",
+
+  // ==================== 06 Knowledge / 知识库 ====================
+  // 01 - Knowledge Base
+  KNOWLEDGE_NOT_FOUND: "060101",
+  KNOWLEDGE_UPLOAD_FAILED: "060102",
+  KNOWLEDGE_SYNC_FAILED: "060103",
+  INDEX_NOT_FOUND: "060104",
+  KNOWLEDGE_SEARCH_FAILED: "060105",
+
+  // ==================== 07 MCPTools / MCP 工具 ====================
+  // 01 - Tool
+  TOOL_NOT_FOUND: "070101",
+  TOOL_EXECUTION_FAILED: "070102",
+  TOOL_CONFIG_INVALID: "070103",
+
+  // 02 - Connection
+  MCP_CONNECTION_FAILED: "070201",
+  MCP_CONTAINER_ERROR: "070202",
+
+  // 03 - Configuration
+  MCP_NAME_ILLEGAL: "070301",
+
+  // ==================== 08 MonitorOps / 监控与运维 ====================
+  // 01 - Monitoring
+  MONITOROPS_METRIC_QUERY_FAILED: "080101",
+
+  // 02 - Alert
+  MONITOROPS_ALERT_CONFIG_INVALID: "080201",
+
+  // ==================== 09 Model / 模型管理 ====================
+  // 01 - Model
+  MODEL_NOT_FOUND: "090101",
+  MODEL_CONFIG_INVALID: "090102",
+  MODEL_HEALTH_CHECK_FAILED: "090103",
+  MODEL_PROVIDER_ERROR: "090104",
+
+  // ==================== 10 Memory / 记忆管理 ====================
+  // 01 - Memory
+  MEMORY_NOT_FOUND: "100101",
+  MEMORY_PREPARATION_FAILED: "100102",
+  MEMORY_CONFIG_INVALID: "100103",
+
+  // ==================== 11 Profile / 个人信息 ====================
+  // 01 - User
+  USER_NOT_FOUND: "110101",
+  USER_UPDATE_FAILED: "110102",
+  USER_ALREADY_EXISTS: "110103",
+  INVALID_CREDENTIALS: "110104",
+
+  // ==================== 12 TenantResource / 租户资源 ====================
+  // 01 - Tenant
+  TENANT_NOT_FOUND: "120101",
+  TENANT_DISABLED: "120102",
+  TENANT_CONFIG_ERROR: "120103",
+  TENANT_RESOURCE_EXCEEDED: "120104",
+
+  // ==================== 13 External / 外部服务 ====================
+  // 01 - DataMate
+  DATAMATE_CONNECTION_FAILED: "130101",
+
+  // 02 - Dify
+  DIFY_SERVICE_ERROR: "130201",
+  DIFY_CONFIG_INVALID: "130202",
+  DIFY_CONNECTION_ERROR: "130203",
+  DIFY_AUTH_ERROR: "130204",
+  DIFY_RATE_LIMIT: "130205",
+  DIFY_RESPONSE_ERROR: "130206",
+
+  // 03 - ME Service
+  ME_CONNECTION_FAILED: "130301",
+
+  // ==================== 14 Northbound / 北向接口 ====================
+  // 01 - Request
+  NORTHBOUND_REQUEST_FAILED: "140101",
+
+  // 02 - Configuration
+  NORTHBOUND_CONFIG_INVALID: "140201",
+
+  // ==================== 15 DataProcess / 数据处理 ====================
+  // 01 - Task
+  DATA_PROCESS_FAILED: "150101",
+  DATA_PARSE_FAILED: "150102",
+
+  // ==================== 99 System / 系统级 ====================
+  // 01 - System Errors
+  UNKNOWN_ERROR: "990101",
+  SERVICE_UNAVAILABLE: "990102",
+  DATABASE_ERROR: "990103",
+  TIMEOUT: "990104",
+  INTERNAL_ERROR: "990105",
+
+  // 02 - Config
+  CONFIG_NOT_FOUND: "990201",
+  CONFIG_UPDATE_FAILED: "990202",
+
+  // ==================== Success Code ====================
+  SUCCESS: "0",
+} as const;
+
+export type ErrorCodeType = typeof ErrorCode[keyof typeof ErrorCode];
+
+/**
+ * Check if an error code represents a success.
+ */
+export const isSuccess = (code: string | number): boolean => {
+  return code === ErrorCode.SUCCESS || code === 0;
+};
+
+/**
+ * Check if an error code represents an authentication error.
+ */
+export const isAuthError = (code: string | number): boolean => {
+  const codeStr = String(code);
+  return codeStr >= "000201" && codeStr < "000300";
+};
+
+/**
+ * Check if an error code represents a session expiration.
+ */
+export const isSessionExpired = (code: string | number): boolean => {
+  return code === ErrorCode.TOKEN_EXPIRED || code === ErrorCode.TOKEN_INVALID;
+};
diff --git a/frontend/const/errorMessage.ts b/frontend/const/errorMessage.ts
new file mode 100644
index 000000000..90ae1c286
--- /dev/null
+++ b/frontend/const/errorMessage.ts
@@ -0,0 +1,212 @@
+/**
+ * Error message utility functions.
+ *
+ * This module provides functions to get error messages by error code.
+ * For i18n support, use the getI18nErrorMessage function which reads from translation files.
+ */
+
+import { ErrorCode } from "./errorCode";
+
+/**
+ * Default error messages (English).
+ * These are fallback messages when i18n is not available.
+ * Must match backend/consts/error_message.py
+ */
+export const DEFAULT_ERROR_MESSAGES: Record<string, string> = {
+  // ==================== 00 Common / 公共 ====================
+  // 01 - Parameter & Validation
+  [ErrorCode.VALIDATION_ERROR]: "Validation error.",
+  [ErrorCode.PARAMETER_INVALID]: "Invalid parameter.",
+  [ErrorCode.MISSING_REQUIRED_FIELD]: "Required field is missing.",
+
+  // 02 - Auth & Permission
+  [ErrorCode.UNAUTHORIZED]: "You are not authorized to perform this action.",
+  [ErrorCode.FORBIDDEN]: "Access forbidden.",
+  [ErrorCode.TOKEN_EXPIRED]: "Your session has expired. Please login again.",
+  [ErrorCode.TOKEN_INVALID]: "Invalid token. Please login again.",
+
+  // 03 - External Service
+  [ErrorCode.EXTERNAL_SERVICE_ERROR]: "External service error.",
+  [ErrorCode.RATE_LIMIT_EXCEEDED]: "Too many requests. Please try again later.",
+
+  // 04 - File
+  [ErrorCode.FILE_NOT_FOUND]: "File not found.",
+  [ErrorCode.FILE_UPLOAD_FAILED]: "Failed to upload file.",
+  [ErrorCode.FILE_TOO_LARGE]: "File size exceeds limit.",
+  [ErrorCode.FILE_TYPE_NOT_ALLOWED]: "File type not allowed.",
+  [ErrorCode.FILE_PREPROCESS_FAILED]: "File preprocessing failed.",
+
+  // 05 - Resource
+  [ErrorCode.RESOURCE_NOT_FOUND]: "Resource not found.",
+  [ErrorCode.RESOURCE_ALREADY_EXISTS]: "Resource already exists.",
+  [ErrorCode.RESOURCE_DISABLED]: "Resource is disabled.",
+
+  // ==================== 01 Chat / 开始问答 ====================
+  // 01 - Conversation
+  [ErrorCode.CONVERSATION_NOT_FOUND]: "Conversation not found.",
+  [ErrorCode.MESSAGE_NOT_FOUND]: "Message not found.",
+  [ErrorCode.CONVERSATION_SAVE_FAILED]: "Failed to save conversation.",
+  [ErrorCode.CONVERSATION_TITLE_GENERATION_FAILED]:
+    "Failed to generate conversation title.",
+
+  // ==================== 02 QuickConfig / 快速配置 ====================
+  // 01 - Configuration
+  [ErrorCode.QUICK_CONFIG_INVALID]: "Invalid configuration.",
+  [ErrorCode.QUICK_CONFIG_SYNC_FAILED]: "Sync configuration failed.",
+
+  // ==================== 03 AgentSpace / 智能体空间 ====================
+  // 01 - Agent
+  [ErrorCode.AGENT_NOT_FOUND]: "Agent not found.",
+  [ErrorCode.AGENT_DISABLED]: "Agent is disabled.",
+  [ErrorCode.AGENT_RUN_FAILED]: "Failed to run agent. Please try again later.",
+  [ErrorCode.AGENT_NAME_DUPLICATE]: "Agent name already exists.",
+  [ErrorCode.AGENT_VERSION_NOT_FOUND]: "Agent version not found.",
+
+  // ==================== 04 AgentMarket / 智能体市场 ====================
+  // 01 - Agent
+  [ErrorCode.AGENTMARKET_AGENT_NOT_FOUND]: "Agent not found in market.",
+
+  // ==================== 05 AgentDev / 智能体开发 ====================
+  // 01 - Configuration
+  [ErrorCode.AGENTDEV_CONFIG_INVALID]: "Invalid agent configuration.",
+  [ErrorCode.AGENTDEV_PROMPT_INVALID]: "Invalid prompt.",
+
+  // ==================== 06 Knowledge / 知识库 ====================
+  // 01 - Knowledge Base
+  [ErrorCode.KNOWLEDGE_NOT_FOUND]: "Knowledge base not found.",
+  [ErrorCode.KNOWLEDGE_UPLOAD_FAILED]: "Failed to upload knowledge.",
+  [ErrorCode.KNOWLEDGE_SYNC_FAILED]: "Failed to sync knowledge base.",
+  [ErrorCode.INDEX_NOT_FOUND]: "Search index not found.",
+  [ErrorCode.KNOWLEDGE_SEARCH_FAILED]: "Knowledge search failed.",
+
+  // ==================== 07 MCPTools / MCP 工具 ====================
+  // 01 - Tool
+  [ErrorCode.TOOL_NOT_FOUND]: "Tool not found.",
+  [ErrorCode.TOOL_EXECUTION_FAILED]: "Tool execution failed.",
+  [ErrorCode.TOOL_CONFIG_INVALID]: "Tool configuration is invalid.",
+
+  // 02 - Connection
+  [ErrorCode.MCP_CONNECTION_FAILED]: "Failed to connect to MCP service.",
+  [ErrorCode.MCP_CONTAINER_ERROR]: "MCP container operation failed.",
+
+  // 03 - Configuration
+  [ErrorCode.MCP_NAME_ILLEGAL]: "MCP name contains invalid characters.",
+
+  // ==================== 08 MonitorOps / 监控与运维 ====================
+  // 01 - Monitoring
+  [ErrorCode.MONITOROPS_METRIC_QUERY_FAILED]: "Metric query failed.",
+
+  // 02 - Alert
+  [ErrorCode.MONITOROPS_ALERT_CONFIG_INVALID]: "Invalid alert configuration.",
+
+  // ==================== 09 Model / 模型管理 ====================
+  // 01 - Model
+  [ErrorCode.MODEL_NOT_FOUND]: "Model not found.",
+  [ErrorCode.MODEL_CONFIG_INVALID]: "Model configuration is invalid.",
+  [ErrorCode.MODEL_HEALTH_CHECK_FAILED]: "Model health check failed.",
+  [ErrorCode.MODEL_PROVIDER_ERROR]: "Model provider error.",
+
+  // ==================== 10 Memory / 记忆管理 ====================
+  // 01 - Memory
+  [ErrorCode.MEMORY_NOT_FOUND]: "Memory not found.",
+  [ErrorCode.MEMORY_PREPARATION_FAILED]: "Failed to prepare memory.",
+  [ErrorCode.MEMORY_CONFIG_INVALID]: "Memory configuration is invalid.",
+
+  // ==================== 11 Profile / 个人信息 ====================
+  // 01 - User
+  [ErrorCode.USER_NOT_FOUND]: "User not found.",
+  [ErrorCode.USER_UPDATE_FAILED]: "Profile update failed.",
+  [ErrorCode.USER_ALREADY_EXISTS]: "User already exists.",
+  [ErrorCode.INVALID_CREDENTIALS]: "Invalid username or password.",
+
+  // ==================== 12 TenantResource / 租户资源 ====================
+  // 01 - Tenant
+  [ErrorCode.TENANT_NOT_FOUND]: "Tenant not found.",
+  [ErrorCode.TENANT_DISABLED]: "Tenant is disabled.",
+  [ErrorCode.TENANT_CONFIG_ERROR]: "Tenant configuration error.",
+  [ErrorCode.TENANT_RESOURCE_EXCEEDED]: "Tenant resource exceeded.",
+
+  // ==================== 13 External / 外部服务 ====================
+  // 01 - DataMate
+  [ErrorCode.DATAMATE_CONNECTION_FAILED]:
+    "Failed to connect to DataMate service.",
+
+  // 02 - Dify
+  [ErrorCode.DIFY_SERVICE_ERROR]: "Dify service error.",
+  [ErrorCode.DIFY_CONFIG_INVALID]:
+    "Dify configuration invalid. Please check URL and API key format.",
+  [ErrorCode.DIFY_CONNECTION_ERROR]:
+    "Failed to connect to Dify. Please check network connection and URL.",
+  [ErrorCode.DIFY_AUTH_ERROR]:
+    "Dify authentication failed. Please check your API key.",
+  [ErrorCode.DIFY_RATE_LIMIT]:
+    "Dify API rate limit exceeded. Please try again later.",
+  [ErrorCode.DIFY_RESPONSE_ERROR]:
+    "Failed to parse Dify response. Please check API URL.",
+
+  // 03 - ME Service
+  [ErrorCode.ME_CONNECTION_FAILED]: "Failed to connect to ME service.",
+
+  // ==================== 14 Northbound / 北向接口 ====================
+  // 01 - Request
+  [ErrorCode.NORTHBOUND_REQUEST_FAILED]: "Northbound request failed.",
+
+  // 02 - Configuration
+  [ErrorCode.NORTHBOUND_CONFIG_INVALID]: "Invalid northbound configuration.",
+
+  // ==================== 15 DataProcess / 数据处理 ====================
+  // 01 - Task
+  [ErrorCode.DATA_PROCESS_FAILED]: "Data processing failed.",
+  [ErrorCode.DATA_PARSE_FAILED]: "Data parsing failed.",
+
+  // ==================== 99 System / 系统级 ====================
+  // 01 - System Errors
+  [ErrorCode.UNKNOWN_ERROR]: "An unknown error occurred. Please try again later.",
+  [ErrorCode.SERVICE_UNAVAILABLE]:
+    "Service is temporarily unavailable. Please try again later.",
+  [ErrorCode.DATABASE_ERROR]:
+    "Database operation failed. Please try again later.",
+  [ErrorCode.TIMEOUT]: "Operation timed out. Please try again later.",
+  [ErrorCode.INTERNAL_ERROR]: "Internal server error. Please try again later.",
+
+  // 02 - Config
+  [ErrorCode.CONFIG_NOT_FOUND]: "Configuration not found.",
+  [ErrorCode.CONFIG_UPDATE_FAILED]: "Configuration update failed.",
+
+  // ==================== Success ====================
+  [ErrorCode.SUCCESS]: "Success",
+};
+
+/**
+ * Get error message by error code.
+ *
+ * @param code - The error code (string or number)
+ * @returns The error message
+ */
+export const getErrorMessage = (code: string | number): string => {
+  const key = String(code);
+  return (
+    DEFAULT_ERROR_MESSAGES[key] || "An error occurred. Please try again later."
+  );
+};
+
+/**
+ * API Response interface.
+ */
+export interface ApiResponse<T = any> {
+  code: number;
+  message: string;
+  data?: T;
+  trace_id?: string;
+  details?: any;
+}
+
+/**
+ * Check if API response indicates success.
+ *
+ * @param response - The API response
+ * @returns True if success
+ */
+export const isApiSuccess = (response: ApiResponse): boolean => {
+  return response.code === 0;;
+}
diff --git a/frontend/const/errorMessageI18n.ts b/frontend/const/errorMessageI18n.ts
new file mode 100644
index 000000000..1c21257f7
--- /dev/null
+++ b/frontend/const/errorMessageI18n.ts
@@ -0,0 +1,238 @@
+/**
+ * Error message utility with i18n support.
+ *
+ * This module provides functions to get localized error messages by error code.
+ */
+
+import { message } from "antd";
+import { useTranslation } from "react-i18next";
+import { ErrorCode } from "./errorCode";
+import { DEFAULT_ERROR_MESSAGES } from "./errorMessage";
+import { handleSessionExpired } from "@/lib/session";
+import { isSessionExpired } from "./errorCode";
+import log from "@/lib/logger";
+
+/**
+ * Get error message by error code with i18n support.
+ *
+ * This function tries to get the message from i18n translation files first,
+ * then falls back to default English messages.
+ *
+ * @param code - The error code
+ * @param t - Optional translation function (if not provided, returns default message)
+ * @returns The localized error message
+ */
+export const getI18nErrorMessage = (
+  code: string | number,
+  t?: (key: string) => string
+): string => {
+  // Try i18n translation first
+  if (t) {
+    const i18nKey = `errorCode.${code}`;
+    const translated = t(i18nKey);
+    // Check if translation exists (i18next returns the key if not found)
+    if (translated !== i18nKey) {
+      return translated;
+    }
+  }
+
+  // Fall back to default message
+  return (
+    DEFAULT_ERROR_MESSAGES[code] ||
+    DEFAULT_ERROR_MESSAGES[ErrorCode.UNKNOWN_ERROR]
+  );
+};
+
+/**
+ * Hook to get error message with i18n support.
+ *
+ * @returns A function that takes an error code and returns the localized message
+ */
+export const useErrorMessage = () => {
+  const { t } = useTranslation();
+
+  return (code: string | number) => getI18nErrorMessage(code, t);
+};
+
+/**
+ * Handle API error and return user-friendly message.
+ *
+ * @param error - The error object (can be ApiError, Error, or any)
+ * @param t - Optional translation function
+ * @returns User-friendly error message
+ */
+export const handleApiError = (
+  error: any,
+  t?: (key: string) => string
+): string => {
+  // Handle ApiError with code
+  if (error && typeof error === "object" && "code" in error) {
+    return getI18nErrorMessage(error.code as string | number, t);
+  }
+
+  // Handle standard Error
+  if (error instanceof Error) {
+    return error.message;
+  }
+
+  // Handle unknown error
+  return getI18nErrorMessage(ErrorCode.UNKNOWN_ERROR, t);
+};
+
+/**
+ * Options for showing error to user
+ */
+export interface ShowErrorOptions {
+  /** Whether to handle session expiration */
+  handleSession?: boolean;
+  /** Whether to show error message (default: true) */
+  showMessage?: boolean;
+  /** Custom error message (overrides auto-detected message) */
+  customMessage?: string;
+  /** Callback after error is shown */
+  onError?: (error: any) => void;
+}
+
+/**
+ * Show error to user with i18n support.
+ *
+ * This is a convenience function that:
+ * 1. Extracts the error code from the error object
+ * 2. Gets the i18n translated message
+ * 3. Shows the message to user via antd message
+ * 4. Optionally handles session expiration
+ *
+ * @param error - The error object (ApiError, Error, or any)
+ * @param t - Translation function (optional, will use default if not provided)
+ * @param options - Additional options
+ *
+ * @example
+ * // Simple usage
+ * showErrorToUser(error);
+ *
+ * @example
+ * // With translation function
+ * const { t } = useTranslation();
+ * showErrorToUser(error, t);
+ *
+ * @example
+ * // With options
+ * showErrorToUser(error, t, { handleSession: true, onError: (e) => console.log(e) });
+ */
+export const showErrorToUser = (
+  error: any,
+  t?: (key: string) => string,
+  options: ShowErrorOptions = {}
+): void => {
+  const {
+    handleSession = true,
+    showMessage = true,
+    customMessage,
+    onError,
+  } = options;
+
+  // Get error code if available
+  let errorCode: number | undefined;
+  if (error && typeof error === "object" && "code" in error) {
+    errorCode = error.code as number;
+  }
+
+  // Handle session expiration
+  if (handleSession && errorCode && isSessionExpired(errorCode)) {
+    handleSessionExpired();
+  }
+
+  // Get the error message
+  let errorMessage: string;
+  if (customMessage) {
+    errorMessage = customMessage;
+  } else if (errorCode) {
+    errorMessage = getI18nErrorMessage(errorCode, t);
+  } else if (error instanceof Error) {
+    errorMessage = error.message;
+  } else {
+    errorMessage = getI18nErrorMessage(ErrorCode.UNKNOWN_ERROR, t);
+  }
+
+  // Log the error
+  log.error(`Error [${errorCode || "unknown"}]: ${errorMessage}`, error);
+
+  // Show message to user
+  if (showMessage) {
+    message.error(errorMessage);
+  }
+
+  // Call onError callback
+  if (onError) {
+    onError(error);
+  }
+};
+
+/**
+ * Wrap an async function with automatic error handling.
+ *
+ * @param fn - The async function to wrap
+ * @param options - Error handling options
+ * @returns Wrapped function that automatically handles errors
+ *
+ * @example
+ * const safeFetchData = withErrorHandler(async () => {
+ *   const result = await api.fetchData();
+ *   return result;
+ * }, { handleSession: true });
+ *
+ * // Usage
+ * await safeFetchData();
+ */
+export const withErrorHandler = (
+  fn: (...args: any[]) => Promise<any>,
+  options: ShowErrorOptions = {}
+) => {
+  return async (...args: any[]) => {
+    try {
+      return await fn(...args);
+    } catch (error) {
+      showErrorToUser(error, undefined, options);
+      throw error;
+    }
+  };
+};
+
+/**
+ * Check if error requires session refresh action.
+ *
+ * @param code - The error code
+ * @returns True if user needs to re-login
+ */
+export const requiresSessionRefresh = (code: string | number): boolean => {
+  const codeStr = String(code);
+  return codeStr === ErrorCode.TOKEN_EXPIRED || codeStr === ErrorCode.TOKEN_INVALID;
+};
+
+/**
+ * Check if error is a validation error.
+ *
+ * @param code - The error code
+ * @returns True if it's a validation error
+ */
+export const isValidationError = (code: string | number): boolean => {
+  const codeStr = String(code);
+  return codeStr >= "000101" && codeStr < "000200";  // 00 Common - 01 Parameter & Validation
+};
+
+/**
+ * Check if error is a resource not found error.
+ *
+ * @param code - The error code
+ * @returns True if resource not found
+ */
+export const isNotFoundError = (code: string | number): boolean => {
+  const codeStr = String(code);
+  return (
+    codeStr === ErrorCode.RESOURCE_NOT_FOUND ||
+    codeStr === ErrorCode.AGENT_NOT_FOUND ||
+    codeStr === ErrorCode.USER_NOT_FOUND ||
+    codeStr === ErrorCode.FILE_NOT_FOUND ||
+    codeStr === ErrorCode.KNOWLEDGE_NOT_FOUND
+  );
+};
diff --git a/frontend/hooks/useErrorHandler.ts b/frontend/hooks/useErrorHandler.ts
new file mode 100644
index 000000000..eb8e57477
--- /dev/null
+++ b/frontend/hooks/useErrorHandler.ts
@@ -0,0 +1,167 @@
+/**
+ * Custom hook for handling API errors with i18n support.
+ *
+ * This hook provides utilities to:
+ * - Convert error codes to localized messages
+ * - Handle session expiration
+ * - Provide consistent error handling across the app
+ */
+
+import { useCallback } from "react";
+import { useTranslation } from "react-i18next";
+import { message } from "antd";
+
+import { ErrorCode, isSessionExpired } from "@/const/errorCode";
+import { DEFAULT_ERROR_MESSAGES } from "@/const/errorMessage";
+import { ApiError } from "@/services/api";
+import { handleSessionExpired } from "@/lib/session";
+import log from "@/lib/logger";
+
+/**
+ * Options for error handling
+ */
+export interface ErrorHandlerOptions {
+  /** Whether to show error message to user */
+  showMessage?: boolean;
+  /** Custom error message key prefix */
+  messagePrefix?: string;
+  /** Callback on error */
+  onError?: (error: Error) => void;
+  /** Whether to handle session expiration */
+  handleSession?: boolean;
+}
+
+/**
+ * Default error handler options
+ */
+const DEFAULT_OPTIONS: ErrorHandlerOptions = {
+  showMessage: true,
+  handleSession: true,
+};
+
+/**
+ * Hook for handling API errors with i18n support
+ */
+export const useErrorHandler = () => {
+  const { t } = useTranslation();
+
+  /**
+   * Get i18n error message by error code
+   */
+  const getI18nErrorMessage = useCallback(
+    (code: string | number): string => {
+      // Try to get i18n key
+      const i18nKey = `errorCode.${code}`;
+      const translated = t(i18nKey);
+
+      // If translation exists (not equal to key), return translated message
+      if (translated !== i18nKey) {
+        return translated;
+      }
+
+      // Fallback to default messages
+      return (
+        DEFAULT_ERROR_MESSAGES[code] ||
+        DEFAULT_ERROR_MESSAGES[ErrorCode.UNKNOWN_ERROR]
+      );
+    },
+    [t]
+  );
+
+  /**
+   * Handle API error
+   */
+  const handleError = useCallback(
+    (error: unknown, options: ErrorHandlerOptions = {}) => {
+      const { showMessage, onError, handleSession } = {
+        ...DEFAULT_OPTIONS,
+        ...options,
+      };
+
+      // Handle ApiError
+      if (error instanceof ApiError) {
+        // Handle session expiration
+        if (handleSession && isSessionExpired(error.code)) {
+          handleSessionExpired();
+        }
+
+        // Get localized message
+        const errorMessage = getI18nErrorMessage(error.code);
+
+        // Log error
+        log.error(`API Error [${error.code}]: ${errorMessage}`, error);
+
+        // Show message to user
+        if (showMessage) {
+          message.error(errorMessage);
+        }
+
+        // Call onError callback
+        if (onError) {
+          onError(error);
+        }
+
+        return {
+          code: error.code,
+          message: errorMessage,
+          originalError: error,
+        };
+      }
+
+      // Handle unknown error
+      if (error instanceof Error) {
+        log.error("Unknown error:", error);
+
+        if (showMessage) {
+          message.error(getI18nErrorMessage(ErrorCode.UNKNOWN_ERROR));
+        }
+
+        if (onError) {
+          onError(error);
+        }
+
+        return {
+          code: ErrorCode.UNKNOWN_ERROR,
+          message: getI18nErrorMessage(ErrorCode.UNKNOWN_ERROR),
+          originalError: error,
+        };
+      }
+
+      // Handle non-Error objects
+      log.error("Non-error object thrown:", error);
+
+      if (showMessage) {
+        message.error(getI18nErrorMessage(ErrorCode.UNKNOWN_ERROR));
+      }
+
+      return {
+        code: ErrorCode.UNKNOWN_ERROR,
+        message: getI18nErrorMessage(ErrorCode.UNKNOWN_ERROR),
+        originalError: null,
+      };
+    },
+    [getI18nErrorMessage]
+  );
+
+  /**
+   * Wrap async function with error handling
+   */
+  const withErrorHandler = useCallback(
+    (fn: (...args: any[]) => Promise<any>, options: ErrorHandlerOptions = {}) => {
+      return async (...args: any[]) => {
+        try {
+          return await fn(...args);
+        } catch (error) {
+          throw handleError(error, options);
+        }
+      };
+    },
+    [handleError]
+  );
+
+  return {
+    getI18nErrorMessage,
+    handleError,
+    withErrorHandler,
+  };
+};
diff --git a/frontend/hooks/useKnowledgeBaseSelector.ts b/frontend/hooks/useKnowledgeBaseSelector.ts
index b3f5de554..a38102291 100644
--- a/frontend/hooks/useKnowledgeBaseSelector.ts
+++ b/frontend/hooks/useKnowledgeBaseSelector.ts
@@ -2,10 +2,12 @@
 
 import { useState, useCallback } from "react";
 import { useQuery, useQueryClient } from "@tanstack/react-query";
+import { useTranslation } from "react-i18next";
 
 import knowledgeBaseService from "@/services/knowledgeBaseService";
 import { KnowledgeBase } from "@/types/knowledgeBase";
 import log from "@/lib/logger";
+import { showErrorToUser } from "@/const/errorMessageI18n";
 
 /**
  * Query key factory for knowledge bases
@@ -34,6 +36,8 @@ export function useKnowledgeBasesForToolConfig(
     apiKey?: string;
   }
 ) {
+  const { t } = useTranslation();
+
   // Support both difyConfig and datamateConfig naming conventions
   const difyConfig = config;
   const datamateConfig = config;
@@ -94,8 +98,10 @@ export function useKnowledgeBasesForToolConfig(
               difyConfig.serverUrl,
               difyConfig.apiKey
             );
-          } catch (error) {
+          } catch (error: any) {
             log.error("Failed to fetch Dify knowledge bases:", error);
+            // Show i18n error message to user
+            showErrorToUser(error, t);
             kbs = [];
           }
         } else {
@@ -130,6 +136,7 @@ export function useKnowledgeBasesForToolConfig(
  * Call this when the user navigates to the agent config page
  */
 export function usePrefetchKnowledgeBases() {
+  const { t } = useTranslation();
   const queryClient = useQueryClient();
 
   const prefetchKnowledgeBases = useCallback(
@@ -194,8 +201,10 @@ export function usePrefetchKnowledgeBases() {
                   difyConfig.serverUrl,
                   difyConfig.apiKey
                 );
-              } catch (error) {
+              } catch (error: any) {
                 log.error("Failed to prefetch Dify knowledge bases:", error);
+                // Show i18n error message to user
+                showErrorToUser(error, t);
                 kbs = [];
               }
             } else {
@@ -225,6 +234,7 @@ export function usePrefetchKnowledgeBases() {
  * Hook for syncing knowledge bases by tool type
  */
 export function useSyncKnowledgeBases() {
+  const { t } = useTranslation();
   const [isSyncing, setIsSyncing] = useState<string | null>(null);
 
   const syncKnowledgeBases = useCallback(
@@ -261,6 +271,10 @@ export function useSyncKnowledgeBases() {
             // Default sync behavior - sync Nexent only
             await knowledgeBaseService.getKnowledgeBasesInfo(false, false);
         }
+      } catch (error: any) {
+        log.error("Failed to sync knowledge bases:", error);
+        // Show i18n error message to user
+        showErrorToUser(error, t);
       } finally {
         setIsSyncing(null);
       }
diff --git a/frontend/public/locales/en/common.json b/frontend/public/locales/en/common.json
index 4d8cefd0a..e69033126 100644
--- a/frontend/public/locales/en/common.json
+++ b/frontend/public/locales/en/common.json
@@ -1779,5 +1779,165 @@
   "agent.version.statusUpdateError": "Failed to update version status",
   "agent.version.needTwoVersions": "At least two versions are required to compare",
   "agent.version.selectDifferentVersions": "Please select two different versions to compare",
-  "agent.error.agentNotFound": "Agent not found"
+  "agent.error.agentNotFound": "Agent not found",
+
+  "errorCode.101001": "An unknown error occurred. Please try again later.",
+  "errorCode.101002": "Service is temporarily unavailable. Please try again later.",
+  "errorCode.101003": "Database operation failed. Please try again later.",
+  "errorCode.101004": "Operation timed out. Please try again later.",
+  "errorCode.101005": "Internal server error. Please try again later.",
+  "errorCode.102001": "You are not authorized to perform this action.",
+  "errorCode.102002": "Your session has expired. Please login again.",
+  "errorCode.102003": "Invalid token. Please login again.",
+  "errorCode.102004": "Request signature verification failed.",
+  "errorCode.102005": "Access forbidden.",
+  "errorCode.103001": "User not found.",
+  "errorCode.103002": "User registration failed. Please try again later.",
+  "errorCode.103003": "User already exists.",
+  "errorCode.103004": "Invalid username or password.",
+  "errorCode.104001": "Tenant not found.",
+  "errorCode.104002": "Tenant is disabled.",
+  "errorCode.104003": "Tenant configuration error.",
+  "errorCode.105001": "Agent not found.",
+  "errorCode.105002": "Failed to run agent. Please try again later.",
+  "errorCode.105003": "Agent name already exists.",
+  "errorCode.105004": "Agent is disabled.",
+  "errorCode.105005": "Agent version not found.",
+  "errorCode.106001": "Tool not found.",
+  "errorCode.106002": "Tool execution failed.",
+  "errorCode.106003": "Tool configuration is invalid.",
+  "errorCode.106101": "Failed to connect to MCP service.",
+  "errorCode.106102": "MCP name contains invalid characters.",
+  "errorCode.106103": "MCP container operation failed.",
+  "errorCode.107001": "Conversation not found.",
+  "errorCode.107002": "Failed to save conversation.",
+  "errorCode.107003": "Message not found.",
+  "errorCode.107004": "Failed to generate conversation title.",
+  "errorCode.108001": "Memory not found.",
+  "errorCode.108002": "Failed to prepare memory.",
+  "errorCode.108003": "Memory configuration is invalid.",
+  "errorCode.109001": "Knowledge base not found.",
+  "errorCode.109002": "Failed to sync knowledge base.",
+  "errorCode.109003": "Search index not found.",
+  "errorCode.109004": "Knowledge search failed.",
+  "errorCode.109005": "Failed to upload knowledge.",
+  "errorCode.110001": "Model not found.",
+  "errorCode.110002": "Model configuration is invalid.",
+  "errorCode.110003": "Model health check failed.",
+  "errorCode.110004": "Model provider error.",
+  "errorCode.111001": "Voice service error.",
+  "errorCode.111002": "Failed to connect to speech recognition service.",
+  "errorCode.111003": "Failed to connect to speech synthesis service.",
+  "errorCode.111004": "Voice configuration is invalid.",
+  "errorCode.112001": "File not found.",
+  "errorCode.112002": "Failed to upload file.",
+  "errorCode.112003": "File size exceeds limit.",
+  "errorCode.112004": "File type not allowed.",
+  "errorCode.112005": "File preprocessing failed.",
+  "errorCode.113001": "Invite code not found.",
+  "errorCode.113002": "Invalid invite code.",
+  "errorCode.113003": "Invite code has expired.",
+  "errorCode.114001": "Group not found.",
+  "errorCode.114002": "Group already exists.",
+  "errorCode.114003": "Member is not in the group.",
+  "errorCode.115001": "Data processing failed.",
+  "errorCode.115002": "Data parsing failed.",
+  "errorCode.130101": "Failed to connect to DataMate service.",
+  "errorCode.130201": "Dify service error.",
+  "errorCode.130202": "Dify configuration invalid. Please check URL and API key format.",
+  "errorCode.130203": "Failed to connect to Dify. Please check network connection and URL.",
+  "errorCode.130204": "Dify authentication failed. Please check your API key.",
+  "errorCode.130205": "Dify API rate limit exceeded. Please try again later.",
+  "errorCode.130206": "Failed to parse Dify response. Please check API URL.",
+  "errorCode.130301": "Failed to connect to ME service.",
+
+  "errorCode.101": "Validation failed.",
+  "errorCode.102": "Invalid parameter.",
+  "errorCode.103": "Required field is missing.",
+
+  "errorCode.201": "You are not authorized to perform this action.",
+  "errorCode.202": "Access forbidden.",
+  "errorCode.203": "Your session has expired. Please login again.",
+  "errorCode.204": "Invalid token. Please login again.",
+
+  "errorCode.301": "External service error.",
+  "errorCode.302": "Too many requests. Please try again later.",
+
+  "errorCode.401": "File not found.",
+  "errorCode.402": "Failed to upload file.",
+  "errorCode.403": "File size exceeds limit.",
+  "errorCode.404": "File type not allowed.",
+  "errorCode.405": "File preprocessing failed.",
+
+  "errorCode.501": "Resource not found.",
+  "errorCode.502": "Resource already exists.",
+  "errorCode.503": "Resource is disabled.",
+
+  "errorCode.10101": "Conversation not found.",
+  "errorCode.10102": "Message not found.",
+  "errorCode.10103": "Failed to save conversation.",
+  "errorCode.10104": "Failed to generate conversation title.",
+
+  "errorCode.20101": "Invalid configuration.",
+  "errorCode.20102": "Sync configuration failed.",
+
+  "errorCode.30101": "Agent not found.",
+  "errorCode.30102": "Agent is disabled.",
+  "errorCode.30103": "Failed to run agent. Please try again later.",
+  "errorCode.30104": "Agent name already exists.",
+  "errorCode.30105": "Agent version not found.",
+
+  "errorCode.40101": "Agent not found in market.",
+
+  "errorCode.50101": "Invalid agent configuration.",
+  "errorCode.50102": "Invalid prompt.",
+
+  "errorCode.60101": "Knowledge base not found.",
+  "errorCode.60102": "Failed to upload knowledge.",
+  "errorCode.60103": "Failed to sync knowledge base.",
+  "errorCode.60104": "Search index not found.",
+  "errorCode.60105": "Knowledge search failed.",
+
+  "errorCode.70101": "Tool not found.",
+  "errorCode.70102": "Tool execution failed.",
+  "errorCode.70103": "Tool configuration is invalid.",
+  "errorCode.70201": "Failed to connect to MCP service.",
+  "errorCode.70202": "MCP container operation failed.",
+  "errorCode.70301": "MCP name contains invalid characters.",
+
+  "errorCode.80101": "Metric query failed.",
+  "errorCode.80201": "Invalid alert configuration.",
+
+  "errorCode.90101": "Model not found.",
+  "errorCode.90102": "Model configuration is invalid.",
+  "errorCode.90103": "Model health check failed.",
+  "errorCode.90104": "Model provider error.",
+
+  "errorCode.100101": "Memory not found.",
+  "errorCode.100102": "Failed to prepare memory.",
+  "errorCode.100103": "Memory configuration is invalid.",
+
+  "errorCode.110101": "User not found.",
+  "errorCode.110102": "Profile update failed.",
+  "errorCode.110103": "User already exists.",
+  "errorCode.110104": "Invalid username or password.",
+
+  "errorCode.120101": "Tenant not found.",
+  "errorCode.120102": "Tenant is disabled.",
+  "errorCode.120103": "Tenant configuration error.",
+  "errorCode.120104": "Tenant resource exceeded.",
+
+  "errorCode.140101": "Northbound request failed.",
+  "errorCode.140201": "Invalid northbound configuration.",
+
+  "errorCode.150101": "Data processing failed.",
+  "errorCode.150102": "Data parsing failed.",
+
+  "errorCode.990101": "An unknown error occurred. Please try again later.",
+  "errorCode.990102": "Service is temporarily unavailable. Please try again later.",
+  "errorCode.990103": "Database operation failed. Please try again later.",
+  "errorCode.990104": "Operation timed out. Please try again later.",
+  "errorCode.990105": "Internal server error. Please try again later.",
+  "errorCode.990201": "Configuration not found.",
+  "errorCode.990202": "Configuration update failed."
 }
diff --git a/frontend/public/locales/zh/common.json b/frontend/public/locales/zh/common.json
index e5c65e03b..7b16eea84 100644
--- a/frontend/public/locales/zh/common.json
+++ b/frontend/public/locales/zh/common.json
@@ -1781,5 +1781,180 @@
   "agent.version.statusUpdateError": "更新版本状态失败",
   "agent.version.needTwoVersions": "至少需要两个版本才能进行对比",
   "agent.version.selectDifferentVersions": "请选择两个不同的版本进行对比",
-  "agent.error.agentNotFound": "未找到智能体"
+  "agent.error.agentNotFound": "未找到智能体",
+
+  "errorCode.101001": "发生未知错误，请稍后重试",
+  "errorCode.101002": "服务暂时不可用，请稍后重试",
+  "errorCode.101003": "数据库操作失败，请稍后重试",
+  "errorCode.101004": "操作超时，请稍后重试",
+  "errorCode.101005": "服务器内部错误，请稍后重试",
+
+  "errorCode.102001": "您没有执行此操作的权限",
+  "errorCode.102002": "您的登录已过期，请重新登录",
+  "errorCode.102003": "登录令牌无效，请重新登录",
+  "errorCode.102004": "请求签名验证失败",
+  "errorCode.102005": "禁止访问",
+
+  "errorCode.103001": "用户不存在",
+  "errorCode.103002": "用户注册失败，请稍后重试",
+  "errorCode.103003": "用户已存在",
+  "errorCode.103004": "用户名或密码错误",
+
+  "errorCode.104001": "租户不存在",
+  "errorCode.104002": "租户已被禁用",
+  "errorCode.104003": "租户配置错误",
+
+  "errorCode.105001": "智能体不存在",
+  "errorCode.105002": "运行智能体失败，请稍后重试",
+  "errorCode.105003": "智能体名称已存在",
+  "errorCode.105004": "智能体已被禁用",
+  "errorCode.105005": "智能体版本不存在",
+
+  "errorCode.106001": "工具不存在",
+  "errorCode.106002": "工具执行失败",
+  "errorCode.106003": "工具配置无效",
+  "errorCode.106101": "连接MCP服务失败",
+  "errorCode.106102": "MCP名称包含非法字符",
+  "errorCode.106103": "MCP容器操作失败",
+
+  "errorCode.107001": "对话不存在",
+  "errorCode.107002": "保存对话失败",
+  "errorCode.107003": "消息不存在",
+  "errorCode.107004": "生成对话标题失败",
+
+  "errorCode.108001": "记忆不存在",
+  "errorCode.108002": "准备记忆失败",
+  "errorCode.108003": "记忆配置无效",
+
+  "errorCode.109001": "知识库不存在",
+  "errorCode.109002": "同步知识库失败",
+  "errorCode.109003": "搜索索引不存在",
+  "errorCode.109004": "知识搜索失败",
+  "errorCode.109005": "上传知识失败",
+
+  "errorCode.110001": "模型不存在",
+  "errorCode.110002": "模型配置无效",
+  "errorCode.110003": "模型健康检查失败",
+  "errorCode.110004": "模型提供商错误",
+
+  "errorCode.111001": "语音服务错误",
+  "errorCode.111002": "连接语音识别服务失败",
+  "errorCode.111003": "连接语音合成服务失败",
+  "errorCode.111004": "语音配置无效",
+
+  "errorCode.112001": "文件不存在",
+  "errorCode.112002": "文件上传失败",
+  "errorCode.112003": "文件大小超出限制",
+  "errorCode.112004": "不支持的文件类型",
+  "errorCode.112005": "文件预处理失败",
+
+  "errorCode.113001": "邀请码不存在",
+  "errorCode.113002": "邀请码无效",
+  "errorCode.113003": "邀请码已过期",
+
+  "errorCode.114001": "群组不存在",
+  "errorCode.114002": "群组已存在",
+  "errorCode.114003": "成员不在群组中",
+
+  "errorCode.115001": "数据处理失败",
+  "errorCode.115002": "数据解析失败",
+
+  "errorCode.130101": "连接DataMate服务失败",
+  "errorCode.130201": "Dify服务错误",
+  "errorCode.130202": "Dify配置无效，请检查URL和API Key格式",
+  "errorCode.130203": "连接Dify失败，请检查网络和URL",
+  "errorCode.130204": "Dify认证失败，请检查API Key",
+  "errorCode.130205": "Dify请求频率超限，请稍后重试",
+  "errorCode.130206": "Dify响应解析失败，请检查API URL",
+  "errorCode.130301": "连接ME服务失败",
+
+  "errorCode.101": "验证失败",
+  "errorCode.102": "参数无效",
+  "errorCode.103": "缺少必填字段",
+
+  "errorCode.201": "您没有执行此操作的权限",
+  "errorCode.202": "禁止访问",
+  "errorCode.203": "您的登录已过期，请重新登录",
+  "errorCode.204": "登录令牌无效，请重新登录",
+
+  "errorCode.301": "外部服务错误",
+  "errorCode.302": "请求过于频繁，请稍后重试",
+
+  "errorCode.401": "文件不存在",
+  "errorCode.402": "文件上传失败",
+  "errorCode.403": "文件大小超出限制",
+  "errorCode.404": "不支持的文件类型",
+  "errorCode.405": "文件预处理失败",
+
+  "errorCode.501": "资源不存在",
+  "errorCode.502": "资源已存在",
+  "errorCode.503": "资源已被禁用",
+
+  "errorCode.10101": "对话不存在",
+  "errorCode.10102": "消息不存在",
+  "errorCode.10103": "保存对话失败",
+  "errorCode.10104": "生成对话标题失败",
+
+  "errorCode.20101": "配置无效",
+  "errorCode.20102": "同步配置失败",
+
+  "errorCode.30101": "智能体不存在",
+  "errorCode.30102": "智能体已被禁用",
+  "errorCode.30103": "运行智能体失败，请稍后重试",
+  "errorCode.30104": "智能体名称已存在",
+  "errorCode.30105": "智能体版本不存在",
+
+  "errorCode.40101": "市场中智能体不存在",
+
+  "errorCode.50101": "智能体配置无效",
+  "errorCode.50102": "提示词无效",
+
+  "errorCode.60101": "知识库不存在",
+  "errorCode.60102": "上传知识失败",
+  "errorCode.60103": "同步知识库失败",
+  "errorCode.60104": "搜索索引不存在",
+  "errorCode.60105": "知识搜索失败",
+
+  "errorCode.70101": "工具不存在",
+  "errorCode.70102": "工具执行失败",
+  "errorCode.70103": "工具配置无效",
+  "errorCode.70201": "连接MCP服务失败",
+  "errorCode.70202": "MCP容器操作失败",
+  "errorCode.70301": "MCP名称包含非法字符",
+
+  "errorCode.80101": "指标查询失败",
+  "errorCode.80201": "告警配置无效",
+
+  "errorCode.90101": "模型不存在",
+  "errorCode.90102": "模型配置无效",
+  "errorCode.90103": "模型健康检查失败",
+  "errorCode.90104": "模型提供商错误",
+
+  "errorCode.100101": "记忆不存在",
+  "errorCode.100102": "准备记忆失败",
+  "errorCode.100103": "记忆配置无效",
+
+  "errorCode.110101": "用户不存在",
+  "errorCode.110102": "更新用户信息失败",
+  "errorCode.110103": "用户已存在",
+  "errorCode.110104": "用户名或密码错误",
+
+  "errorCode.120101": "租户不存在",
+  "errorCode.120102": "租户已被禁用",
+  "errorCode.120103": "租户配置错误",
+  "errorCode.120104": "租户资源超限",
+
+  "errorCode.140101": "北向接口请求失败",
+  "errorCode.140201": "北向接口配置无效",
+
+  "errorCode.150101": "数据处理失败",
+  "errorCode.150102": "数据解析失败",
+
+  "errorCode.990101": "发生未知错误，请稍后重试",
+  "errorCode.990102": "服务暂时不可用，请稍后重试",
+  "errorCode.990103": "数据库操作失败，请稍后重试",
+  "errorCode.990104": "操作超时，请稍后重试",
+  "errorCode.990105": "服务器内部错误，请稍后重试",
+  "errorCode.990201": "配置不存在",
+  "errorCode.990202": "配置更新失败"
 }
diff --git a/frontend/services/api.ts b/frontend/services/api.ts
index 3237905ed..31174e830 100644
--- a/frontend/services/api.ts
+++ b/frontend/services/api.ts
@@ -1,4 +1,5 @@
 import { STATUS_CODES } from "@/const/auth";
+import { ErrorCode } from "@/const/errorCode";
 import { handleSessionExpired } from "@/lib/session";
 import log from "@/lib/logger";
 import type { MarketAgentListParams } from "@/types/market";
@@ -301,7 +302,7 @@ export const API_ENDPOINTS = {
 // Common error handling
 export class ApiError extends Error {
   constructor(
-    public code: number,
+    public code: string | number,
     message: string
   ) {
     super(message);
@@ -319,20 +320,42 @@ export const fetchWithErrorHandling = async (
 
     // Handle HTTP errors
     if (!response.ok) {
-      // Check if it's a session expired error (401)
-      if (response.status === 401) {
+      // Try to parse JSON response for business error code first
+      let errorCode = response.status;
+      let errorMessage = `Request failed: ${response.status}`;
+      const errorText = await response.text();
+
+      let parsedErrorData = null;
+      try {
+        const errorData = JSON.parse(errorText);
+        if (errorData && errorData.code) {
+          parsedErrorData = errorData;
+          errorCode = errorData.code;
+          errorMessage = errorData.message || errorMessage;
+        } else {
+          errorMessage = errorText || errorMessage;
+        }
+      } catch {
+        // Not JSON, use text as message
+        errorMessage = errorText || errorMessage;
+      }
+
+      // Check if it's a session expiration error based on business error code
+      // TOKEN_EXPIRED = "000203", TOKEN_INVALID = "000204"
+      const errorCodeStr = String(errorCode);
+      if (
+        errorCodeStr === ErrorCode.TOKEN_EXPIRED ||
+        errorCodeStr === ErrorCode.TOKEN_INVALID
+      ) {
         handleSessionExpired();
-        throw new ApiError(
-          STATUS_CODES.TOKEN_EXPIRED,
-          "Login expired, please login again"
-        );
+        throw new ApiError(errorCode, errorMessage);
       }
 
       // Handle custom 499 error code (client closed connection)
       if (response.status === 499) {
         handleSessionExpired();
         throw new ApiError(
-          STATUS_CODES.TOKEN_EXPIRED,
+          ErrorCode.TOKEN_EXPIRED,
           "Connection disconnected, session may have expired"
         );
       }
@@ -340,17 +363,12 @@ export const fetchWithErrorHandling = async (
       // Handle request entity too large error (413)
       if (response.status === 413) {
         throw new ApiError(
-          STATUS_CODES.REQUEST_ENTITY_TOO_LARGE,
-          "REQUEST_ENTITY_TOO_LARGE"
+          ErrorCode.FILE_TOO_LARGE,
+          "File size exceeds limit."
         );
       }
 
-      // Other HTTP errors
-      const errorText = await response.text();
-      throw new ApiError(
-        response.status,
-        errorText || `Request failed: ${response.status}`
-      );
+      throw new ApiError(errorCode, errorMessage);
     }
 
     return response;
diff --git a/frontend/services/knowledgeBaseService.ts b/frontend/services/knowledgeBaseService.ts
index 0fe76ced7..5558eabd0 100644
--- a/frontend/services/knowledgeBaseService.ts
+++ b/frontend/services/knowledgeBaseService.ts
@@ -2,7 +2,7 @@
 
 import i18n from "i18next";
 
-import { API_ENDPOINTS } from "./api";
+import { API_ENDPOINTS, ApiError } from "./api";
 
 import { NAME_CHECK_STATUS } from "@/const/agentConfig";
 import { FILE_TYPES, EXTENSION_TO_TYPE_MAP } from "@/const/knowledgeBase";
@@ -53,32 +53,35 @@ class KnowledgeBaseService {
     count: number;
     indices_info: any[];
   }> {
-    try {
-      // Call backend proxy endpoint to avoid CORS issues
-      const url = new URL(API_ENDPOINTS.dify.datasets, window.location.origin);
-      url.searchParams.set("dify_api_base", difyApiBase);
-      url.searchParams.set("api_key", apiKey);
-
-      const response = await fetch(url.toString(), {
-        method: "GET",
-        headers: getAuthHeaders(),
-      });
-
-      if (!response.ok) {
-        const errorData = await response.json();
-        throw new Error(errorData.detail || "Failed to fetch Dify datasets");
-      }
-
-      const result = await response.json();
-      return {
-        indices: result.indices || [],
-        count: result.count || 0,
-        indices_info: result.indices_info || [],
-      };
-    } catch (error) {
-      log.error("Failed to sync Dify knowledge bases:", error);
-      throw error;
+    // Call backend proxy endpoint to avoid CORS issues
+    const url = new URL(API_ENDPOINTS.dify.datasets, window.location.origin);
+    url.searchParams.set("dify_api_base", difyApiBase);
+    url.searchParams.set("api_key", apiKey);
+
+    const response = await fetch(url.toString(), {
+      method: "GET",
+      headers: getAuthHeaders(),
+    });
+
+    const result = await response.json();
+
+    // Check for error response from middleware (has code field)
+    if (result.code !== undefined && result.code !== 0) {
+      // Use backend error code and message
+      const errorCode = result.code || response.status;
+      const errorMessage = result.message || "Failed to fetch Dify datasets";
+      log.error("Dify API error:", { code: errorCode, message: errorMessage });
+
+      // Use ApiError for proper error handling with i18n support
+      throw new ApiError(errorCode, errorMessage);
     }
+
+    // Success: result is directly the data (indices, count, indices_info)
+    return {
+      indices: result.indices || [],
+      count: result.count || 0,
+      indices_info: result.indices_info || [],
+    };
   }
 
   // Get Dify knowledge bases as KnowledgeBase array
diff --git a/test/backend/app/test_app_factory.py b/test/backend/app/test_app_factory.py
new file mode 100644
index 000000000..0e46cae7b
--- /dev/null
+++ b/test/backend/app/test_app_factory.py
@@ -0,0 +1,701 @@
+"""
+Unit tests for app_factory module.
+
+Tests the create_app function and register_exception_handlers function
+for FastAPI application factory with common configurations and exception handlers.
+"""
+import sys
+import os
+
+from fastapi import FastAPI, HTTPException
+from fastapi.testclient import TestClient
+
+# Add the backend directory to path so we can import modules
+backend_path = os.path.abspath(os.path.join(
+    os.path.dirname(__file__), '../../../backend'))
+sys.path.insert(0, backend_path)
+
+# Import AppException from consts.exceptions where it is defined
+from consts.error_code import ErrorCode
+from consts.exceptions import AppException
+from backend.apps.app_factory import create_app, register_exception_handlers
+
+class TestCreateApp:
+    """Test class for create_app function."""
+
+    def test_create_app_default_parameters(self):
+        """Test creating app with default parameters."""
+        app = create_app()
+
+        assert app is not None
+        assert isinstance(app, FastAPI)
+        assert app.title == "Nexent API"
+        assert app.version == "1.0.0"
+        assert app.root_path == "/api"
+
+    def test_create_app_custom_title(self):
+        """Test creating app with custom title."""
+        app = create_app(title="Custom API")
+
+        assert app.title == "Custom API"
+
+    def test_create_app_custom_description(self):
+        """Test creating app with custom description."""
+        app = create_app(description="Custom description")
+
+        assert app.description == "Custom description"
+
+    def test_create_app_custom_version(self):
+        """Test creating app with custom version."""
+        app = create_app(version="2.0.0")
+
+        assert app.version == "2.0.0"
+
+    def test_create_app_custom_root_path(self):
+        """Test creating app with custom root path."""
+        app = create_app(root_path="/custom")
+
+        assert app.root_path == "/custom"
+
+    def test_create_app_custom_cors_origins(self):
+        """Test creating app with custom CORS origins."""
+        custom_origins = ["https://example.com", "https://api.example.com"]
+        app = create_app(cors_origins=custom_origins)
+
+        assert app is not None
+
+    def test_create_app_custom_cors_methods(self):
+        """Test creating app with custom CORS methods."""
+        custom_methods = ["GET", "POST", "PUT", "DELETE"]
+        app = create_app(cors_methods=custom_methods)
+
+        assert app is not None
+
+    def test_create_app_with_monitoring_disabled(self):
+        """Test creating app with monitoring disabled."""
+        app = create_app(enable_monitoring=False)
+
+        assert app is not None
+        assert isinstance(app, FastAPI)
+
+    def test_create_app_with_monitoring_enabled(self):
+        """Test creating app with monitoring enabled."""
+        app = create_app(enable_monitoring=True)
+
+        assert app is not None
+        assert isinstance(app, FastAPI)
+
+    def test_create_app_all_parameters(self):
+        """Test creating app with all parameters."""
+        app = create_app(
+            title="Full Test API",
+            description="Full description",
+            version="3.0.0",
+            root_path="/v3",
+            cors_origins=["https://test.com"],
+            cors_methods=["GET", "POST"],
+            enable_monitoring=True
+        )
+
+        assert app.title == "Full Test API"
+        assert app.description == "Full description"
+        assert app.version == "3.0.0"
+        assert app.root_path == "/v3"
+
+
+class TestRegisterExceptionHandlers:
+    """Test class for register_exception_handlers function."""
+
+    def test_register_exception_handlers_basic(self):
+        """Test registering exception handlers on a basic FastAPI app."""
+        app = FastAPI()
+        register_exception_handlers(app)
+
+        assert app is not None
+
+    def test_http_exception_handler(self):
+        """Test HTTPException handler returns correct response."""
+        app = FastAPI()
+        register_exception_handlers(app)
+
+        @app.get("/test-http-exception")
+        def raise_http_exception():
+            raise HTTPException(status_code=404, detail="Not found")
+
+        client = TestClient(app, raise_server_exceptions=False)
+        response = client.get("/test-http-exception")
+
+        assert response.status_code == 404
+        assert response.json() == {"message": "Not found"}
+
+    def test_http_exception_handler_400(self):
+        """Test HTTPException handler with 400 status."""
+        app = FastAPI()
+        register_exception_handlers(app)
+
+        @app.get("/test-bad-request")
+        def raise_bad_request():
+            raise HTTPException(status_code=400, detail="Bad request")
+
+        client = TestClient(app, raise_server_exceptions=False)
+        response = client.get("/test-bad-request")
+
+        assert response.status_code == 400
+        assert response.json() == {"message": "Bad request"}
+
+    def test_http_exception_handler_500(self):
+        """Test HTTPException handler with 500 status."""
+        app = FastAPI()
+        register_exception_handlers(app)
+
+        @app.get("/test-server-error")
+        def raise_server_error():
+            raise HTTPException(
+                status_code=500, detail="Internal server error")
+
+        client = TestClient(app, raise_server_exceptions=False)
+        response = client.get("/test-server-error")
+
+        assert response.status_code == 500
+        assert response.json() == {"message": "Internal server error"}
+
+    def test_app_exception_handler(self):
+        """Test AppException handler returns correct response."""
+        app = FastAPI()
+        register_exception_handlers(app)
+
+        @app.get("/test-app-exception")
+        def raise_app_exception():
+            raise AppException(
+                ErrorCode.COMMON_VALIDATION_ERROR, "Validation failed")
+
+        client = TestClient(app, raise_server_exceptions=False)
+        response = client.get("/test-app-exception")
+
+        assert response.status_code == 400
+        assert response.json()[
+            "code"] == ErrorCode.COMMON_VALIDATION_ERROR.value
+        assert response.json()["message"] == "Validation failed"
+
+    def test_app_exception_handler_with_details(self):
+        """Test AppException handler with details returns correct response."""
+        app = FastAPI()
+        register_exception_handlers(app)
+
+        @app.get("/test-app-exception-details")
+        def raise_app_exception_with_details():
+            raise AppException(
+                ErrorCode.MCP_CONNECTION_FAILED,
+                "Connection failed",
+                details={"host": "localhost", "port": 8080}
+            )
+
+        client = TestClient(app, raise_server_exceptions=False)
+        response = client.get("/test-app-exception-details")
+
+        # MCP_CONNECTION_FAILED maps to 500 by default
+        assert response.status_code == 500
+        assert response.json()["code"] == ErrorCode.MCP_CONNECTION_FAILED.value
+        assert response.json()["details"] == {
+            "host": "localhost", "port": 8080}
+
+    def test_app_exception_handler_unauthorized(self):
+        """Test AppException handler with UNAUTHORIZED error code."""
+        app = FastAPI()
+        register_exception_handlers(app)
+
+        @app.get("/test-unauthorized")
+        def raise_unauthorized():
+            raise AppException(ErrorCode.COMMON_UNAUTHORIZED,
+                               "Unauthorized access")
+
+        client = TestClient(app, raise_server_exceptions=False)
+        response = client.get("/test-unauthorized")
+
+        assert response.status_code == 401
+
+    def test_app_exception_handler_forbidden(self):
+        """Test AppException handler with FORBIDDEN error code."""
+        app = FastAPI()
+        register_exception_handlers(app)
+
+        @app.get("/test-forbidden")
+        def raise_forbidden():
+            raise AppException(ErrorCode.COMMON_FORBIDDEN, "Access forbidden")
+
+        client = TestClient(app, raise_server_exceptions=False)
+        response = client.get("/test-forbidden")
+
+        assert response.status_code == 403
+
+    def test_app_exception_handler_rate_limit(self):
+        """Test AppException handler with RATE_LIMIT_EXCEEDED error code."""
+        app = FastAPI()
+        register_exception_handlers(app)
+
+        @app.get("/test-rate-limit")
+        def raise_rate_limit():
+            raise AppException(ErrorCode.COMMON_RATE_LIMIT_EXCEEDED,
+                               "Too many requests")
+
+        client = TestClient(app, raise_server_exceptions=False)
+        response = client.get("/test-rate-limit")
+
+        assert response.status_code == 429
+
+    def test_generic_exception_handler(self):
+        """Test generic Exception handler returns correct response."""
+        app = FastAPI()
+        register_exception_handlers(app)
+
+        @app.get("/test-generic-exception")
+        def raise_generic_exception():
+            raise RuntimeError("Something went wrong")
+
+        client = TestClient(app, raise_server_exceptions=False)
+        response = client.get("/test-generic-exception")
+
+        assert response.status_code == 500
+        assert response.json() == {
+            "message": "Internal server error, please try again later."}
+
+    def test_generic_exception_handler_value_error(self):
+        """Test generic Exception handler with ValueError."""
+        app = FastAPI()
+        register_exception_handlers(app)
+
+        @app.get("/test-value-error")
+        def raise_value_error():
+            raise ValueError("Invalid value")
+
+        client = TestClient(app, raise_server_exceptions=False)
+        response = client.get("/test-value-error")
+
+        assert response.status_code == 500
+
+    def test_app_exception_takes_precedence_in_generic_handler(self):
+        """Test that AppException is handled by its own handler, not generic."""
+        app = FastAPI()
+        register_exception_handlers(app)
+
+        @app.get("/test-app-exception-in-generic")
+        def raise_app_exception():
+            # This should be handled by AppException handler, not generic
+            # Use VALIDATION_ERROR which maps to 400
+            raise AppException(
+                ErrorCode.COMMON_VALIDATION_ERROR, "Validation failed")
+
+        client = TestClient(app, raise_server_exceptions=False)
+        response = client.get("/test-app-exception-in-generic")
+
+        # Should return 400 (mapped from VALIDATION_ERROR)
+        assert response.status_code == 400
+        assert response.json()[
+            "code"] == ErrorCode.COMMON_VALIDATION_ERROR.value
+
+
+class TestExceptionMappingToHttpStatus:
+    """Test class for exception mapping to HTTP status codes."""
+
+    def test_validation_error_maps_to_400(self):
+        """Test VALIDATION_ERROR maps to 400."""
+        app = FastAPI()
+        register_exception_handlers(app)
+
+        @app.get("/validation-error")
+        def test_validation():
+            raise AppException(
+                ErrorCode.COMMON_VALIDATION_ERROR, "Invalid input")
+
+        client = TestClient(app, raise_server_exceptions=False)
+        response = client.get("/validation-error")
+
+        assert response.status_code == 400
+
+    def test_parameter_invalid_maps_to_400(self):
+        """Test PARAMETER_INVALID maps to 400."""
+        app = FastAPI()
+        register_exception_handlers(app)
+
+        @app.get("/parameter-invalid")
+        def test_param():
+            raise AppException(ErrorCode.COMMON_PARAMETER_INVALID,
+                               "Invalid parameter")
+
+        client = TestClient(app, raise_server_exceptions=False)
+        response = client.get("/parameter-invalid")
+
+        assert response.status_code == 400
+
+    def test_missing_required_field_maps_to_400(self):
+        """Test MISSING_REQUIRED_FIELD maps to 400."""
+        app = FastAPI()
+        register_exception_handlers(app)
+
+        @app.get("/missing-field")
+        def test_missing():
+            raise AppException(
+                ErrorCode.COMMON_MISSING_REQUIRED_FIELD, "Field missing")
+
+        client = TestClient(app, raise_server_exceptions=False)
+        response = client.get("/missing-field")
+
+        assert response.status_code == 400
+
+    def test_file_too_large_maps_to_413(self):
+        """Test FILE_TOO_LARGE maps to 413."""
+        app = FastAPI()
+        register_exception_handlers(app)
+
+        @app.get("/file-too-large")
+        def test_file():
+            raise AppException(ErrorCode.FILE_TOO_LARGE, "File too large")
+
+        client = TestClient(app, raise_server_exceptions=False)
+        response = client.get("/file-too-large")
+
+        assert response.status_code == 413
+
+
+class TestMonitoringIntegration:
+    """Test class for monitoring integration."""
+
+    def test_monitoring_enabled_does_not_raise(self):
+        """Test that create_app with enable_monitoring=True does not raise."""
+        # This tests that the monitoring code path runs without error
+        # Even if monitoring is not available, it should be caught gracefully
+        app = create_app(enable_monitoring=True)
+
+        assert app is not None
+        assert isinstance(app, FastAPI)
+
+    def test_monitoring_disabled_does_not_raise(self):
+        """Test that create_app with enable_monitoring=False does not raise."""
+        app = create_app(enable_monitoring=False)
+
+        assert app is not None
+        assert isinstance(app, FastAPI)
+
+    def test_monitoring_with_actual_module(self):
+        """Test that create_app works when monitoring module is available."""
+        # Test with monitoring disabled to avoid actual module dependency
+        app = create_app(enable_monitoring=False)
+
+        assert app is not None
+        # Verify basic app attributes are set correctly
+        assert app.title == "Nexent API"
+        assert app.version == "1.0.0"
+        assert app.root_path == "/api"
+
+
+class TestCORSConfiguration:
+    """Test class for CORS configuration."""
+
+    def test_cors_middleware_added_with_default_origins(self):
+        """Test CORS middleware is added with default origins."""
+        app = create_app()
+
+        # Verify CORS middleware is in the middleware stack
+        # FastAPI adds middleware as wrappers
+        middleware_stack = app.user_middleware
+        assert len(middleware_stack) > 0
+
+    def test_cors_middleware_added_with_custom_origins(self):
+        """Test CORS middleware is added with custom origins."""
+        custom_origins = ["https://example.com"]
+        app = create_app(cors_origins=custom_origins)
+
+        assert app is not None
+
+    def test_cors_middleware_with_credentials(self):
+        """Test CORS middleware allows credentials."""
+        app = create_app()
+
+        # Middleware should be added
+        assert app is not None
+
+
+class TestAppExceptionResponseFormat:
+    """Test class for AppException response format."""
+
+    def test_response_contains_code_field(self):
+        """Test response contains 'code' field."""
+        app = FastAPI()
+        register_exception_handlers(app)
+
+        @app.get("/test-code-field")
+        def test_code():
+            raise AppException(
+                ErrorCode.AGENTSPACE_AGENT_NOT_FOUND, "Agent not found")
+
+        client = TestClient(app, raise_server_exceptions=False)
+        response = client.get("/test-code-field")
+
+        assert "code" in response.json()
+
+    def test_response_contains_message_field(self):
+        """Test response contains 'message' field."""
+        app = FastAPI()
+        register_exception_handlers(app)
+
+        @app.get("/test-message-field")
+        def test_message():
+            raise AppException(
+                ErrorCode.AGENTSPACE_AGENT_NOT_FOUND, "Agent not found")
+
+        client = TestClient(app, raise_server_exceptions=False)
+        response = client.get("/test-message-field")
+
+        assert "message" in response.json()
+
+    def test_response_details_is_none_when_not_provided(self):
+        """Test response details is None when not provided."""
+        app = FastAPI()
+        register_exception_handlers(app)
+
+        @app.get("/test-no-details")
+        def test_no_details():
+            raise AppException(
+                ErrorCode.COMMON_VALIDATION_ERROR, "Validation failed")
+
+        client = TestClient(app, raise_server_exceptions=False)
+        response = client.get("/test-no-details")
+
+        # details should be None when not provided
+        assert response.json().get("details") is None
+
+
+class TestMultipleExceptionHandlers:
+    """Test class for multiple exception handlers in same app."""
+
+    def test_multiple_routes_with_different_exceptions(self):
+        """Test app handles different exception types from different routes."""
+        app = FastAPI()
+        register_exception_handlers(app)
+
+        @app.get("/http-exc")
+        def route_http():
+            raise HTTPException(status_code=400, detail="HTTP error")
+
+        @app.get("/app-exc")
+        def route_app():
+            raise AppException(ErrorCode.COMMON_VALIDATION_ERROR, "App error")
+
+        @app.get("/gen-exc")
+        def route_gen():
+            raise Exception("Generic error")
+
+        client = TestClient(app, raise_server_exceptions=False)
+
+        assert client.get("/http-exc").status_code == 400
+        assert client.get("/app-exc").status_code == 400
+        assert client.get("/gen-exc").status_code == 500
+
+
+class TestMonitoringImportFailure:
+    """Test class for monitoring import failure scenarios.
+
+    Tests the logger.warning when monitoring utilities are not available.
+    """
+
+    def test_create_app_monitoring_import_failure_logs_warning(self):
+        """Test that create_app logs warning when monitoring module import fails."""
+        import logging
+        from unittest.mock import patch, MagicMock
+
+        # Mock the monitoring module to raise ImportError
+        with patch.dict('sys.modules', {'utils.monitoring': None}):
+            with patch('backend.apps.app_factory.logger') as mock_logger:
+                # Create app with monitoring enabled - import will fail
+                app = create_app(enable_monitoring=True)
+
+                # Verify logger.warning was called with expected message
+                mock_logger.warning.assert_called_once_with(
+                    "Monitoring utilities not available"
+                )
+
+                assert app is not None
+                assert isinstance(app, FastAPI)
+
+    def test_create_app_monitoring_disabled_no_warning(self):
+        """Test that no warning is logged when monitoring is disabled."""
+        from unittest.mock import patch
+
+        with patch('backend.apps.app_factory.logger') as mock_logger:
+            app = create_app(enable_monitoring=False)
+
+            # Warning should not be called when monitoring is disabled
+            mock_logger.warning.assert_not_called()
+
+            assert app is not None
+
+    def test_create_app_monitoring_import_error_specific_exception(self):
+        """Test that create_app handles ImportError specifically."""
+        from unittest.mock import patch, MagicMock
+
+        # Create a mock monitoring module that raises ImportError when accessed
+        mock_module = MagicMock()
+        mock_module.monitoring_manager = MagicMock()
+        mock_module.monitoring_manager.setup_fastapi_app.side_effect = ImportError(
+            "No module named 'monitoring'"
+        )
+
+        with patch.dict('sys.modules', {'utils.monitoring': mock_module}):
+            with patch('backend.apps.app_factory.logger') as mock_logger:
+                app = create_app(enable_monitoring=True)
+
+                # Should log warning about monitoring utilities not available
+                mock_logger.warning.assert_called_with(
+                    "Monitoring utilities not available"
+                )
+
+                assert app is not None
+
+
+class TestGenericExceptionHandlerAppExceptionCheck:
+    """Test class for generic exception handler's AppException check.
+
+    Tests the logic that prevents AppException from being caught
+    by the generic Exception handler.
+    """
+
+    def test_generic_handler_does_not_catch_app_exception_with_different_codes(self):
+        """Test that generic handler does not catch AppException for various error codes."""
+        from fastapi.testclient import TestClient
+        from fastapi import FastAPI
+
+        # Test multiple AppException error codes to ensure they're all handled correctly
+        error_codes_to_test = [
+            (ErrorCode.COMMON_VALIDATION_ERROR, 400),
+            (ErrorCode.COMMON_UNAUTHORIZED, 401),
+            (ErrorCode.COMMON_FORBIDDEN, 403),
+            (ErrorCode.COMMON_RESOURCE_NOT_FOUND, 404),
+            (ErrorCode.COMMON_RATE_LIMIT_EXCEEDED, 429),
+        ]
+
+        for error_code, expected_status in error_codes_to_test:
+            app = FastAPI()
+            register_exception_handlers(app)
+
+            @app.get(f"/test-{error_code.value}")
+            def raise_specific_app_exception():
+                raise AppException(error_code, f"Error {error_code.value}")
+
+            client = TestClient(app, raise_server_exceptions=False)
+            response = client.get(f"/test-{error_code.value}")
+
+            # Each AppException should be handled by its specific handler, not generic
+            assert response.status_code == expected_status, \
+                f"Expected {expected_status} for {error_code.value}, got {response.status_code}"
+            assert "code" in response.json()
+            assert response.json()["code"] == error_code.value
+
+    def test_generic_handler_does_catch_non_app_exception(self):
+        """Test that generic handler correctly catches non-AppException errors."""
+        app = FastAPI()
+        register_exception_handlers(app)
+
+        @app.get("/test-runtime-error")
+        def raise_runtime_error():
+            raise RuntimeError("Runtime error occurred")
+
+        client = TestClient(app, raise_server_exceptions=False)
+        response = client.get("/test-runtime-error")
+
+        # Generic exception handler should catch this
+        assert response.status_code == 500
+        assert response.json()[
+            "message"] == "Internal server error, please try again later."
+
+    def test_generic_handler_does_catch_value_error(self):
+        """Test that generic handler catches ValueError."""
+        app = FastAPI()
+        register_exception_handlers(app)
+
+        @app.get("/test-value-error")
+        def raise_value_error():
+            raise ValueError("Invalid value provided")
+
+        client = TestClient(app, raise_server_exceptions=False)
+        response = client.get("/test-value-error")
+
+        # Generic exception handler should catch ValueError
+        assert response.status_code == 500
+        assert response.json()[
+            "message"] == "Internal server error, please try again later."
+
+    def test_generic_handler_does_catch_type_error(self):
+        """Test that generic handler catches TypeError."""
+        app = FastAPI()
+        register_exception_handlers(app)
+
+        @app.get("/test-type-error")
+        def raise_type_error():
+            raise TypeError("Type mismatch")
+
+        client = TestClient(app, raise_server_exceptions=False)
+        response = client.get("/test-type-error")
+
+        # Generic exception handler should catch TypeError
+        assert response.status_code == 500
+
+    def test_app_exception_with_custom_http_status(self):
+        """Test AppException with custom HTTP status is handled correctly."""
+        app = FastAPI()
+        register_exception_handlers(app)
+
+        @app.get("/test-custom-status")
+        def raise_custom_status():
+            # Use an error code that maps to a different status
+            raise AppException(ErrorCode.DIFY_SERVICE_ERROR,
+                               "Dify service error")
+
+        client = TestClient(app, raise_server_exceptions=False)
+        response = client.get("/test-custom-status")
+
+        # DIFY_SERVICE_ERROR is not in the mapping, so it defaults to 500
+        # This test verifies that custom error codes still work correctly
+        assert response.status_code == 500
+        assert response.json()["code"] == ErrorCode.DIFY_SERVICE_ERROR.value
+
+    def test_both_exception_handlers_registered(self):
+        """Test that both AppException and generic Exception handlers are registered."""
+        app = FastAPI()
+        register_exception_handlers(app)
+
+        # Check that exception handlers are registered
+        exception_handlers = app.exception_handlers
+
+        # Both HTTPException and Exception handlers should be registered
+        assert HTTPException in exception_handlers
+        assert Exception in exception_handlers
+
+    def test_app_exception_not_duplicated_in_generic_handler_logs(self):
+        """Test that AppException is not logged as generic exception."""
+        import logging
+        from unittest.mock import patch
+
+        app = FastAPI()
+        register_exception_handlers(app)
+
+        @app.get("/test-app-exc")
+        def raise_app_exc():
+            raise AppException(
+                ErrorCode.COMMON_VALIDATION_ERROR, "Validation error")
+
+        # Use capture to check logging
+        with patch('backend.apps.app_factory.logger') as mock_logger:
+            client = TestClient(app, raise_server_exceptions=False)
+            response = client.get("/test-app-exc")
+
+            # AppException should NOT trigger the generic exception logger
+            # It should go through the app_exception_handler which also logs
+            # But the generic handler should NOT log it as "Generic Exception"
+            assert response.status_code == 400
+
+            # Verify the AppException handler logged it (not generic)
+            # The AppException handler logs: f"AppException: {exc.error_code.value} - {exc.message}"
+            app_exception_logged = any(
+                "AppException:" in str(call) for call in mock_logger.error.call_args_list
+            )
+            assert app_exception_logged, "AppException should be logged by app_exception_handler"
diff --git a/test/backend/app/test_config_app.py b/test/backend/app/test_config_app.py
index 87ca2b959..a4dd4566b 100644
--- a/test/backend/app/test_config_app.py
+++ b/test/backend/app/test_config_app.py
@@ -1,8 +1,13 @@
+import pytest
 import unittest
 from unittest.mock import patch, MagicMock, Mock
 import sys
 import os
 
+from fastapi import HTTPException
+from fastapi.testclient import TestClient
+import atexit
+
 # Add the backend directory to path so we can import modules
 backend_path = os.path.abspath(os.path.join(os.path.dirname(__file__), '../../../backend'))
 sys.path.insert(0, backend_path)
@@ -23,8 +28,10 @@
 # before any module imports that might trigger MinioClient initialization
 critical_patches = [
     # Patch storage factory and MinIO config validation FIRST
-    patch('nexent.storage.storage_client_factory.create_storage_client_from_config', return_value=storage_client_mock),
-    patch('nexent.storage.minio_config.MinIOStorageConfig.validate', lambda self: None),
+    patch('nexent.storage.storage_client_factory.create_storage_client_from_config',
+          return_value=storage_client_mock),
+    patch('nexent.storage.minio_config.MinIOStorageConfig.validate',
+          lambda self: None),
     # Mock boto3 client
     patch('boto3.client', return_value=Mock()),
     # Mock boto3 resource
@@ -54,27 +61,30 @@
 # After import, we can patch get_db_session if needed
 try:
     from backend.database import client as db_client_module
+
     # Patch get_db_session after module is imported
-    db_session_patch = patch.object(db_client_module, 'get_db_session', return_value=Mock())
+    db_session_patch = patch.object(
+        db_client_module, 'get_db_session', return_value=Mock())
     db_session_patch.start()
     all_patches.append(db_session_patch)
 except ImportError:
     # If import fails, try patching the path directly (may trigger import)
-    db_session_patch = patch('backend.database.client.get_db_session', return_value=Mock())
+    db_session_patch = patch(
+        'backend.database.client.get_db_session', return_value=Mock())
     db_session_patch.start()
     all_patches.append(db_session_patch)
 
-# Now safe to import app modules
-from fastapi import HTTPException
-from fastapi.testclient import TestClient
+# Now safe to import app modules - imports moved after patches
 from apps.config_app import app
 
-
 # Stop all patches at the end of the module
-import atexit
+
+
 def stop_patches():
     for p in all_patches:
         p.stop()
+
+
 atexit.register(stop_patches)
 
 
@@ -94,9 +104,9 @@ def test_cors_middleware(self):
             if middleware.cls.__name__ == "CORSMiddleware":
                 cors_middleware = middleware
                 break
-        
+
         self.assertIsNotNone(cors_middleware)
-        
+
         # In FastAPI, middleware options are stored in 'middleware.kwargs'
         self.assertEqual(cors_middleware.kwargs.get("allow_origins"), ["*"])
         self.assertTrue(cors_middleware.kwargs.get("allow_credentials"))
@@ -107,31 +117,10 @@ def test_routers_included(self):
         """Test that all routers are included in the app."""
         # Get all routes in the app
         routes = [route.path for route in app.routes]
-        
+
         # Check if routes exist (at least some routes should be present)
         self.assertTrue(len(routes) > 0)
 
-    def test_http_exception_handler(self):
-        """Test the HTTP exception handler."""
-        # Test that the exception handler is registered
-        exception_handlers = app.exception_handlers
-        self.assertIn(HTTPException, exception_handlers)
-        
-        # Test that the handler function exists and is callable
-        http_exception_handler = exception_handlers[HTTPException]
-        self.assertIsNotNone(http_exception_handler)
-        self.assertTrue(callable(http_exception_handler))
-
-    def test_generic_exception_handler(self):
-        """Test the generic exception handler."""
-        # Test that the exception handler is registered
-        exception_handlers = app.exception_handlers
-        self.assertIn(Exception, exception_handlers)
-        
-        # Test that the handler function exists and is callable
-        generic_exception_handler = exception_handlers[Exception]
-        self.assertTrue(callable(generic_exception_handler))
-
     def test_exception_handling_with_client(self):
         """Test exception handling using the test client."""
         # This test requires mocking an endpoint that raises an exception
@@ -178,7 +167,8 @@ def test_all_routers_included(self):
             'file_manager_router',
             'proxy_router',
             'tool_config_router',
-            'mock_user_management_router',  # or 'user_management_router' depending on IS_SPEED_MODE
+            # or 'user_management_router' depending on IS_SPEED_MODE
+            'mock_user_management_router',
             'summary_router',
             'prompt_router',
             'tenant_config_router',
@@ -197,19 +187,8 @@ def test_all_routers_included(self):
 
         # Since it's hard to identify routers directly from routes,
         # we'll check that we have a reasonable number of routes
-        self.assertGreater(len(app.routes), 10)  # Should have many routes from all routers
-
-    def test_http_exception_handler_registration(self):
-        """Test that HTTP exception handler is properly registered."""
-        # Test that the exception handler exists in the app
-        exception_handlers = app.exception_handlers
-        self.assertIn(HTTPException, exception_handlers)
-
-    def test_generic_exception_handler_registration(self):
-        """Test that generic exception handler is properly registered."""
-        # Test that the exception handler exists in the app
-        exception_handlers = app.exception_handlers
-        self.assertIn(Exception, exception_handlers)
+        # Should have many routes from all routers
+        self.assertGreater(len(app.routes), 10)
 
 
 if __name__ == "__main__":
diff --git a/test/backend/app/test_dify_app.py b/test/backend/app/test_dify_app.py
index ad9c8c53c..63395a868 100644
--- a/test/backend/app/test_dify_app.py
+++ b/test/backend/app/test_dify_app.py
@@ -132,7 +132,8 @@ async def test_fetch_dify_datasets_api_success(self, dify_mocks):
         response_body = json.loads(result.body.decode())
         assert response_body == expected_result
 
-        dify_mocks['get_current_user_id'].assert_called_once_with(mock_auth_header)
+        # Note: get_current_user_id is imported but not used in dify_app.py
+        # The test verifies the actual behavior of the function
         dify_mocks['fetch_dify'].assert_called_once_with(
             dify_api_base=dify_api_base.rstrip('/'),
             api_key=api_key
@@ -172,28 +173,35 @@ async def test_fetch_dify_datasets_api_url_normalization(self, dify_mocks):
     @pytest.mark.asyncio
     async def test_fetch_dify_datasets_api_auth_error(self, dify_mocks):
         """Test endpoint with authentication error."""
+        from consts.exceptions import AppException
+        from consts.error_code import ErrorCode
+
         mock_auth_header = "Bearer invalid-token"
         dify_api_base = "https://dify.example.com"
         api_key = "test-api-key"
 
         # Mock authentication failure
-        dify_mocks['get_current_user_id'].side_effect = Exception("Invalid token")
+        dify_mocks['get_current_user_id'].side_effect = Exception(
+            "Invalid token")
 
-        # Execute and Assert
-        with pytest.raises(HTTPException) as exc_info:
+        # Execute and Assert - the code catches Exception and converts to AppException
+        with pytest.raises(AppException) as exc_info:
             await fetch_dify_datasets_api(
                 dify_api_base=dify_api_base,
                 api_key=api_key,
                 authorization=mock_auth_header
             )
 
-        assert exc_info.value.status_code == HTTPStatus.INTERNAL_SERVER_ERROR
-        assert "Failed to fetch Dify datasets" in str(exc_info.value.detail)
-        dify_mocks['logger'].error.assert_not_called()
+        assert exc_info.value.error_code == ErrorCode.DIFY_SERVICE_ERROR
+        assert "Failed to fetch Dify datasets" in str(exc_info.value.message)
+        dify_mocks['logger'].error.assert_called()
 
     @pytest.mark.asyncio
     async def test_fetch_dify_datasets_api_service_validation_error(self, dify_mocks):
         """Test endpoint with service layer validation error (ValueError)."""
+        from consts.exceptions import AppException
+        from consts.error_code import ErrorCode
+
         mock_auth_header = "Bearer test-token"
         dify_api_base = "https://dify.example.com"
         api_key = ""
@@ -201,21 +209,24 @@ async def test_fetch_dify_datasets_api_service_validation_error(self, dify_mocks
         dify_mocks['get_current_user_id'].return_value = (
             "test_user_id", "test_tenant_id"
         )
-        dify_mocks['fetch_dify'].side_effect = ValueError("api_key is required")
+        dify_mocks['fetch_dify'].side_effect = ValueError(
+            "api_key is required")
 
-        with pytest.raises(HTTPException) as exc_info:
+        with pytest.raises(AppException) as exc_info:
             await fetch_dify_datasets_api(
                 dify_api_base=dify_api_base,
                 api_key=api_key,
                 authorization=mock_auth_header
             )
 
-        assert exc_info.value.status_code == HTTPStatus.BAD_REQUEST
-        assert "api_key is required" in str(exc_info.value.detail)
+        assert exc_info.value.error_code == ErrorCode.DIFY_SERVICE_ERROR
 
     @pytest.mark.asyncio
     async def test_fetch_dify_datasets_api_service_error(self, dify_mocks):
         """Test endpoint with general service layer error."""
+        from consts.exceptions import AppException
+        from consts.error_code import ErrorCode
+
         mock_auth_header = "Bearer test-token"
         dify_api_base = "https://dify.example.com"
         api_key = "test-api-key"
@@ -223,23 +234,27 @@ async def test_fetch_dify_datasets_api_service_error(self, dify_mocks):
         dify_mocks['get_current_user_id'].return_value = (
             "test_user_id", "test_tenant_id"
         )
-        dify_mocks['fetch_dify'].side_effect = Exception("Dify API connection failed")
+        dify_mocks['fetch_dify'].side_effect = Exception(
+            "Dify API connection failed")
 
-        with pytest.raises(HTTPException) as exc_info:
+        with pytest.raises(AppException) as exc_info:
             await fetch_dify_datasets_api(
                 dify_api_base=dify_api_base,
                 api_key=api_key,
                 authorization=mock_auth_header
             )
 
-        assert exc_info.value.status_code == HTTPStatus.INTERNAL_SERVER_ERROR
-        assert "Failed to fetch Dify datasets" in str(exc_info.value.detail)
-        assert "Dify API connection failed" in str(exc_info.value.detail)
+        assert exc_info.value.error_code == ErrorCode.DIFY_SERVICE_ERROR
+        assert "Failed to fetch Dify datasets" in str(exc_info.value.message)
+        assert "Dify API connection failed" in str(exc_info.value.message)
         dify_mocks['logger'].error.assert_called()
 
     @pytest.mark.asyncio
     async def test_fetch_dify_datasets_api_http_error_from_service(self, dify_mocks):
         """Test endpoint when service raises HTTP-related exception."""
+        from consts.exceptions import AppException
+        from consts.error_code import ErrorCode
+
         mock_auth_header = "Bearer test-token"
         dify_api_base = "https://dify.example.com"
         api_key = "test-api-key"
@@ -248,21 +263,25 @@ async def test_fetch_dify_datasets_api_http_error_from_service(self, dify_mocks)
             "test_user_id", "test_tenant_id"
         )
         # Simulate HTTP error from service
-        dify_mocks['fetch_dify'].side_effect = Exception("Dify API HTTP error: 404 Not Found")
+        dify_mocks['fetch_dify'].side_effect = Exception(
+            "Dify API HTTP error: 404 Not Found")
 
-        with pytest.raises(HTTPException) as exc_info:
+        with pytest.raises(AppException) as exc_info:
             await fetch_dify_datasets_api(
                 dify_api_base=dify_api_base,
                 api_key=api_key,
                 authorization=mock_auth_header
             )
 
-        assert exc_info.value.status_code == HTTPStatus.INTERNAL_SERVER_ERROR
-        assert "Failed to fetch Dify datasets" in str(exc_info.value.detail)
+        assert exc_info.value.error_code == ErrorCode.DIFY_SERVICE_ERROR
+        assert "Failed to fetch Dify datasets" in str(exc_info.value.message)
 
     @pytest.mark.asyncio
     async def test_fetch_dify_datasets_api_request_error_from_service(self, dify_mocks):
         """Test endpoint when service raises request error."""
+        from consts.exceptions import AppException
+        from consts.error_code import ErrorCode
+
         mock_auth_header = "Bearer test-token"
         dify_api_base = "https://dify.example.com"
         api_key = "test-api-key"
@@ -271,17 +290,21 @@ async def test_fetch_dify_datasets_api_request_error_from_service(self, dify_moc
             "test_user_id", "test_tenant_id"
         )
         # Simulate request error from service
-        dify_mocks['fetch_dify'].side_effect = Exception("Dify API request failed: Connection refused")
+        dify_mocks['fetch_dify'].side_effect = Exception(
+            "Dify API request failed: Connection refused")
+
+        from consts.exceptions import AppException
+        from consts.error_code import ErrorCode
 
-        with pytest.raises(HTTPException) as exc_info:
+        with pytest.raises(AppException) as exc_info:
             await fetch_dify_datasets_api(
                 dify_api_base=dify_api_base,
                 api_key=api_key,
                 authorization=mock_auth_header
             )
 
-        assert exc_info.value.status_code == HTTPStatus.INTERNAL_SERVER_ERROR
-        assert "Failed to fetch Dify datasets" in str(exc_info.value.detail)
+        assert exc_info.value.error_code == ErrorCode.DIFY_SERVICE_ERROR
+        assert "Failed to fetch Dify datasets" in str(exc_info.value.message)
 
     @pytest.mark.asyncio
     async def test_fetch_dify_datasets_api_none_auth_header(self, dify_mocks):
@@ -297,7 +320,7 @@ async def test_fetch_dify_datasets_api_none_auth_header(self, dify_mocks):
             "pagination": {"embedding_available": False}
         }
 
-        # Mock user and tenant ID for None auth
+        # Mock user and tenant ID for None auth (even though it's not used in the current implementation)
         dify_mocks['get_current_user_id'].return_value = (
             "default_user", "default_tenant"
         )
@@ -312,7 +335,8 @@ async def test_fetch_dify_datasets_api_none_auth_header(self, dify_mocks):
         assert isinstance(result, JSONResponse)
         assert result.status_code == HTTPStatus.OK
 
-        dify_mocks['get_current_user_id'].assert_called_once_with(None)
+        # Note: get_current_user_id is imported but not used in dify_app.py
+        # The test verifies the actual behavior of the function
 
     @pytest.mark.asyncio
     async def test_fetch_dify_datasets_api_empty_result(self, dify_mocks):
@@ -457,6 +481,8 @@ async def test_fetch_dify_datasets_api_logger_info_call(self, dify_mocks):
     @pytest.mark.asyncio
     async def test_fetch_dify_datasets_api_logger_error_call(self, dify_mocks):
         """Test that endpoint logs errors appropriately."""
+        from consts.exceptions import AppException
+
         mock_auth_header = "Bearer test-token"
         dify_api_base = "https://dify.example.com"
         api_key = "test-api-key"
@@ -466,7 +492,7 @@ async def test_fetch_dify_datasets_api_logger_error_call(self, dify_mocks):
         )
         dify_mocks['fetch_dify'].side_effect = Exception("Connection timeout")
 
-        with pytest.raises(HTTPException):
+        with pytest.raises(AppException):
             await fetch_dify_datasets_api(
                 dify_api_base=dify_api_base,
                 api_key=api_key,
@@ -557,3 +583,474 @@ def test_router_has_datasets_endpoint(self):
         routes = [route.path for route in router.routes]
         # Router prefix is /dify, and route is /datasets, so full path is /dify/datasets
         assert "/dify/datasets" in routes
+
+
+class TestDifyAppExceptionHandlers:
+    """Test exception handlers in dify_app.py"""
+
+    def test_dify_app_exception_handler_functions_exist(self):
+        """Test that dify_app module can import exception handlers if defined."""
+        # dify_app.py doesn't define its own exception handlers,
+        # it relies on the global middleware in config_app.py
+        # This test verifies the module structure
+        from backend.apps import dify_app
+        from backend.apps.dify_app import router, logger, fetch_dify_datasets_api
+
+        # Verify router exists
+        assert router is not None
+        # Verify logger exists
+        assert logger is not None
+        # Verify endpoint function exists
+        assert fetch_dify_datasets_api is not None
+
+    @pytest.mark.asyncio
+    async def test_dify_app_logs_service_error(self, dify_mocks):
+        """Test that service errors are logged and converted to AppException."""
+        mock_auth_header = "Bearer test-token"
+        dify_api_base = "https://dify.example.com"
+        api_key = "test-api-key"
+
+        dify_mocks['get_current_user_id'].return_value = (
+            "test_user_id", "test_tenant_id"
+        )
+
+        # Test with service error
+        dify_mocks['fetch_dify'].side_effect = Exception(
+            "URL connection error")
+
+        from consts.exceptions import AppException
+
+        with pytest.raises(AppException) as exc_info:
+            await fetch_dify_datasets_api(
+                dify_api_base=dify_api_base,
+                api_key=api_key,
+                authorization=mock_auth_header
+            )
+
+        # Verify it's a DIFY_SERVICE_ERROR
+        assert "Failed to fetch Dify datasets" in str(exc_info.value.message)
+        dify_mocks['logger'].error.assert_called()
+
+
+class TestFetchDifyDatasetsApiConfigValidation:
+    """Test class for fetch_dify_datasets_api endpoint configuration validation.
+
+    Tests the first try-except block that handles invalid Dify configuration
+    (e.g., when dify_api_base.rstrip('/') fails due to invalid input).
+    """
+
+    @pytest.mark.asyncio
+    async def test_fetch_dify_datasets_api_invalid_dify_api_base_none(self):
+        """Test endpoint raises DIFY_CONFIG_INVALID when dify_api_base is None."""
+        from consts.exceptions import AppException
+        from consts.error_code import ErrorCode
+
+        mock_auth_header = "Bearer test-token"
+        dify_api_base = None
+        api_key = "test-api-key"
+
+        with patch('backend.apps.dify_app.get_current_user_id') as mock_get_current_user_id, \
+                patch('backend.apps.dify_app.fetch_dify_datasets_impl') as mock_fetch_dify, \
+                patch('backend.apps.dify_app.logger') as mock_logger:
+
+            mock_get_current_user_id.return_value = (
+                "test_user_id", "test_tenant_id"
+            )
+
+            with pytest.raises(AppException) as exc_info:
+                await fetch_dify_datasets_api(
+                    dify_api_base=dify_api_base,
+                    api_key=api_key,
+                    authorization=mock_auth_header
+                )
+
+            assert exc_info.value.error_code == ErrorCode.DIFY_CONFIG_INVALID
+            assert "Invalid URL format" in str(exc_info.value.message)
+            mock_logger.error.assert_called()
+            mock_fetch_dify.assert_not_called()
+
+    @pytest.mark.asyncio
+    async def test_fetch_dify_datasets_api_invalid_dify_api_base_integer(self):
+        """Test endpoint raises DIFY_CONFIG_INVALID when dify_api_base is an integer."""
+        from consts.exceptions import AppException
+        from consts.error_code import ErrorCode
+
+        mock_auth_header = "Bearer test-token"
+        dify_api_base = 12345  # Invalid type - should be string
+        api_key = "test-api-key"
+
+        with patch('backend.apps.dify_app.get_current_user_id') as mock_get_current_user_id, \
+                patch('backend.apps.dify_app.fetch_dify_datasets_impl') as mock_fetch_dify, \
+                patch('backend.apps.dify_app.logger') as mock_logger:
+
+            mock_get_current_user_id.return_value = (
+                "test_user_id", "test_tenant_id"
+            )
+
+            with pytest.raises(AppException) as exc_info:
+                await fetch_dify_datasets_api(
+                    dify_api_base=dify_api_base,
+                    api_key=api_key,
+                    authorization=mock_auth_header
+                )
+
+            assert exc_info.value.error_code == ErrorCode.DIFY_CONFIG_INVALID
+            assert "Invalid URL format" in str(exc_info.value.message)
+            mock_logger.error.assert_called()
+            mock_fetch_dify.assert_not_called()
+
+    @pytest.mark.asyncio
+    async def test_fetch_dify_datasets_api_invalid_dify_api_base_object(self):
+        """Test endpoint raises DIFY_CONFIG_INVALID when dify_api_base is an object without rstrip."""
+        from consts.exceptions import AppException
+        from consts.error_code import ErrorCode
+
+        mock_auth_header = "Bearer test-token"
+        # Invalid type - should be string
+        dify_api_base = {"url": "https://dify.example.com"}
+        api_key = "test-api-key"
+
+        with patch('backend.apps.dify_app.get_current_user_id') as mock_get_current_user_id, \
+                patch('backend.apps.dify_app.fetch_dify_datasets_impl') as mock_fetch_dify, \
+                patch('backend.apps.dify_app.logger') as mock_logger:
+
+            mock_get_current_user_id.return_value = (
+                "test_user_id", "test_tenant_id"
+            )
+
+            with pytest.raises(AppException) as exc_info:
+                await fetch_dify_datasets_api(
+                    dify_api_base=dify_api_base,
+                    api_key=api_key,
+                    authorization=mock_auth_header
+                )
+
+            assert exc_info.value.error_code == ErrorCode.DIFY_CONFIG_INVALID
+            mock_logger.error.assert_called()
+            mock_fetch_dify.assert_not_called()
+
+    @pytest.mark.asyncio
+    async def test_fetch_dify_datasets_api_invalid_dify_api_base_list(self):
+        """Test endpoint raises DIFY_CONFIG_INVALID when dify_api_base is a list."""
+        from consts.exceptions import AppException
+        from consts.error_code import ErrorCode
+
+        mock_auth_header = "Bearer test-token"
+        # Invalid type - should be string
+        dify_api_base = ["https://dify.example.com"]
+        api_key = "test-api-key"
+
+        with patch('backend.apps.dify_app.get_current_user_id') as mock_get_current_user_id, \
+                patch('backend.apps.dify_app.fetch_dify_datasets_impl') as mock_fetch_dify, \
+                patch('backend.apps.dify_app.logger') as mock_logger:
+
+            mock_get_current_user_id.return_value = (
+                "test_user_id", "test_tenant_id"
+            )
+
+            with pytest.raises(AppException) as exc_info:
+                await fetch_dify_datasets_api(
+                    dify_api_base=dify_api_base,
+                    api_key=api_key,
+                    authorization=mock_auth_header
+                )
+
+            assert exc_info.value.error_code == ErrorCode.DIFY_CONFIG_INVALID
+            mock_logger.error.assert_called()
+            mock_fetch_dify.assert_not_called()
+
+    @pytest.mark.asyncio
+    async def test_fetch_dify_datasets_api_dify_config_invalid_logs_error_message(self):
+        """Test that DIFY_CONFIG_INVALID error logs the actual exception message."""
+        from consts.exceptions import AppException
+        from consts.error_code import ErrorCode
+
+        mock_auth_header = "Bearer test-token"
+        # This will cause AttributeError: 'NoneType' object has no attribute 'rstrip'
+        dify_api_base = None
+        api_key = "test-api-key"
+
+        with patch('backend.apps.dify_app.get_current_user_id') as mock_get_current_user_id, \
+                patch('backend.apps.dify_app.fetch_dify_datasets_impl') as mock_fetch_dify, \
+                patch('backend.apps.dify_app.logger') as mock_logger:
+
+            mock_get_current_user_id.return_value = (
+                "test_user_id", "test_tenant_id"
+            )
+
+            with pytest.raises(AppException) as exc_info:
+                await fetch_dify_datasets_api(
+                    dify_api_base=dify_api_base,
+                    api_key=api_key,
+                    authorization=mock_auth_header
+                )
+
+            # Verify logger was called with the error
+            mock_logger.error.assert_called_once()
+            call_args = mock_logger.error.call_args
+            assert "Invalid Dify configuration" in call_args[0][0]
+            assert "'NoneType' object has no attribute 'rstrip'" in call_args[
+                0][0] or "NoneType" in call_args[0][0]
+
+    @pytest.mark.asyncio
+    async def test_fetch_dify_datasets_api_success_after_config_validation(self):
+        """Test endpoint succeeds when config validation passes (valid string input)."""
+        mock_auth_header = "Bearer test-token"
+        dify_api_base = "https://dify.example.com"
+        api_key = "test-api-key"
+
+        expected_result = {
+            "indices": ["ds-1"],
+            "count": 1,
+            "indices_info": [],
+            "pagination": {"embedding_available": True}
+        }
+
+        with patch('backend.apps.dify_app.get_current_user_id') as mock_get_current_user_id, \
+                patch('backend.apps.dify_app.fetch_dify_datasets_impl') as mock_fetch_dify, \
+                patch('backend.apps.dify_app.logger') as mock_logger:
+
+            mock_get_current_user_id.return_value = (
+                "test_user_id", "test_tenant_id"
+            )
+            mock_fetch_dify.return_value = expected_result
+
+            result = await fetch_dify_datasets_api(
+                dify_api_base=dify_api_base,
+                api_key=api_key,
+                authorization=mock_auth_header
+            )
+
+            assert isinstance(result, JSONResponse)
+            assert result.status_code == HTTPStatus.OK
+            # Verify the service was called with normalized URL
+            mock_fetch_dify.assert_called_once_with(
+                dify_api_base="https://dify.example.com",
+                api_key=api_key
+            )
+
+
+class TestAppExceptionReRaising:
+    """Test class for AppException re-raising to global middleware.
+
+    Tests the except AppException: raise block that propagates AppException
+    from the service layer to be handled by global middleware.
+    """
+
+    @pytest.mark.asyncio
+    async def test_service_raises_app_exception_re_raised_to_middleware(self):
+        """Test that AppException from service is re-raised for global middleware."""
+        from consts.exceptions import AppException
+        from consts.error_code import ErrorCode
+
+        mock_auth_header = "Bearer test-token"
+        dify_api_base = "https://dify.example.com"
+        api_key = "test-api-key"
+
+        # Create an AppException that the service would raise
+        service_exception = AppException(
+            ErrorCode.DIFY_CONNECTION_ERROR,
+            "Failed to connect to Dify API"
+        )
+
+        with patch('backend.apps.dify_app.get_current_user_id') as mock_get_current_user_id, \
+                patch('backend.apps.dify_app.fetch_dify_datasets_impl') as mock_fetch_dify, \
+                patch('backend.apps.dify_app.logger') as mock_logger:
+
+            mock_get_current_user_id.return_value = (
+                "test_user_id", "test_tenant_id"
+            )
+            mock_fetch_dify.side_effect = service_exception
+
+            # The AppException should be re-raised (not converted)
+            with pytest.raises(AppException) as exc_info:
+                await fetch_dify_datasets_api(
+                    dify_api_base=dify_api_base,
+                    api_key=api_key,
+                    authorization=mock_auth_header
+                )
+
+            # Verify the original AppException is re-raised with its original error code
+            assert exc_info.value.error_code == ErrorCode.DIFY_CONNECTION_ERROR
+            assert "Failed to connect to Dify API" in str(
+                exc_info.value.message)
+
+    @pytest.mark.asyncio
+    async def test_service_raises_dify_config_invalid_app_exception(self):
+        """Test that DIFY_CONFIG_INVALID AppException from service is re-raised."""
+        from consts.exceptions import AppException
+        from consts.error_code import ErrorCode
+
+        mock_auth_header = "Bearer test-token"
+        dify_api_base = "https://dify.example.com"
+        api_key = "test-api-key"
+
+        # Simulate service raising DIFY_CONFIG_INVALID
+        service_exception = AppException(
+            ErrorCode.DIFY_CONFIG_INVALID,
+            "Invalid Dify API key format"
+        )
+
+        with patch('backend.apps.dify_app.get_current_user_id') as mock_get_current_user_id, \
+                patch('backend.apps.dify_app.fetch_dify_datasets_impl') as mock_fetch_dify, \
+                patch('backend.apps.dify_app.logger') as mock_logger:
+
+            mock_get_current_user_id.return_value = (
+                "test_user_id", "test_tenant_id"
+            )
+            mock_fetch_dify.side_effect = service_exception
+
+            # Should re-raise the AppException
+            with pytest.raises(AppException) as exc_info:
+                await fetch_dify_datasets_api(
+                    dify_api_base=dify_api_base,
+                    api_key=api_key,
+                    authorization=mock_auth_header
+                )
+
+            assert exc_info.value.error_code == ErrorCode.DIFY_CONFIG_INVALID
+
+    @pytest.mark.asyncio
+    async def test_service_raises_dify_auth_error_app_exception(self):
+        """Test that DIFY_AUTH_ERROR AppException from service is re-raised."""
+        from consts.exceptions import AppException
+        from consts.error_code import ErrorCode
+
+        mock_auth_header = "Bearer test-token"
+        dify_api_base = "https://dify.example.com"
+        api_key = "test-api-key"
+
+        # Simulate service raising DIFY_AUTH_ERROR
+        service_exception = AppException(
+            ErrorCode.DIFY_AUTH_ERROR,
+            "Invalid API key provided"
+        )
+
+        with patch('backend.apps.dify_app.get_current_user_id') as mock_get_current_user_id, \
+                patch('backend.apps.dify_app.fetch_dify_datasets_impl') as mock_fetch_dify, \
+                patch('backend.apps.dify_app.logger') as mock_logger:
+
+            mock_get_current_user_id.return_value = (
+                "test_user_id", "test_tenant_id"
+            )
+            mock_fetch_dify.side_effect = service_exception
+
+            # Should re-raise the AppException
+            with pytest.raises(AppException) as exc_info:
+                await fetch_dify_datasets_api(
+                    dify_api_base=dify_api_base,
+                    api_key=api_key,
+                    authorization=mock_auth_header
+                )
+
+            assert exc_info.value.error_code == ErrorCode.DIFY_AUTH_ERROR
+
+    @pytest.mark.asyncio
+    async def test_service_raises_app_exception_with_details(self):
+        """Test that AppException with details from service is re-raised."""
+        from consts.exceptions import AppException
+        from consts.error_code import ErrorCode
+
+        mock_auth_header = "Bearer test-token"
+        dify_api_base = "https://dify.example.com"
+        api_key = "test-api-key"
+
+        # AppException with details
+        service_exception = AppException(
+            ErrorCode.DIFY_CONNECTION_ERROR,
+            "Connection failed",
+            details={"host": "dify.example.com", "port": 443}
+        )
+
+        with patch('backend.apps.dify_app.get_current_user_id') as mock_get_current_user_id, \
+                patch('backend.apps.dify_app.fetch_dify_datasets_impl') as mock_fetch_dify, \
+                patch('backend.apps.dify_app.logger') as mock_logger:
+
+            mock_get_current_user_id.return_value = (
+                "test_user_id", "test_tenant_id"
+            )
+            mock_fetch_dify.side_effect = service_exception
+
+            # Should re-raise the AppException with details preserved
+            with pytest.raises(AppException) as exc_info:
+                await fetch_dify_datasets_api(
+                    dify_api_base=dify_api_base,
+                    api_key=api_key,
+                    authorization=mock_auth_header
+                )
+
+            assert exc_info.value.error_code == ErrorCode.DIFY_CONNECTION_ERROR
+            assert exc_info.value.details == {
+                "host": "dify.example.com", "port": 443}
+
+    @pytest.mark.asyncio
+    async def test_service_raises_dify_rate_limit_app_exception(self):
+        """Test that DIFY_RATE_LIMIT AppException from service is re-raised."""
+        from consts.exceptions import AppException
+        from consts.error_code import ErrorCode
+
+        mock_auth_header = "Bearer test-token"
+        dify_api_base = "https://dify.example.com"
+        api_key = "test-api-key"
+
+        # Simulate service raising DIFY_RATE_LIMIT
+        service_exception = AppException(
+            ErrorCode.DIFY_RATE_LIMIT,
+            "Rate limit exceeded"
+        )
+
+        with patch('backend.apps.dify_app.get_current_user_id') as mock_get_current_user_id, \
+                patch('backend.apps.dify_app.fetch_dify_datasets_impl') as mock_fetch_dify, \
+                patch('backend.apps.dify_app.logger') as mock_logger:
+
+            mock_get_current_user_id.return_value = (
+                "test_user_id", "test_tenant_id"
+            )
+            mock_fetch_dify.side_effect = service_exception
+
+            # Should re-raise the AppException
+            with pytest.raises(AppException) as exc_info:
+                await fetch_dify_datasets_api(
+                    dify_api_base=dify_api_base,
+                    api_key=api_key,
+                    authorization=mock_auth_header
+                )
+
+            assert exc_info.value.error_code == ErrorCode.DIFY_RATE_LIMIT
+
+    @pytest.mark.asyncio
+    async def test_app_exception_not_wrapped_or_converted(self):
+        """Test that AppException is not wrapped or converted to another exception."""
+        from consts.exceptions import AppException
+        from consts.error_code import ErrorCode
+
+        mock_auth_header = "Bearer test-token"
+        dify_api_base = "https://dify.example.com"
+        api_key = "test-api-key"
+
+        # Use a non-Dify error code to verify it's not converted
+        service_exception = AppException(
+            ErrorCode.COMMON_UNAUTHORIZED,
+            "Unauthorized access"
+        )
+
+        with patch('backend.apps.dify_app.get_current_user_id') as mock_get_current_user_id, \
+                patch('backend.apps.dify_app.fetch_dify_datasets_impl') as mock_fetch_dify, \
+                patch('backend.apps.dify_app.logger') as mock_logger:
+
+            mock_get_current_user_id.return_value = (
+                "test_user_id", "test_tenant_id"
+            )
+            mock_fetch_dify.side_effect = service_exception
+
+            # Should re-raise the exact same AppException
+            with pytest.raises(AppException) as exc_info:
+                await fetch_dify_datasets_api(
+                    dify_api_base=dify_api_base,
+                    api_key=api_key,
+                    authorization=mock_auth_header
+                )
+
+            # Verify it's the exact same exception instance (not a new one)
+            assert exc_info.value is service_exception
+            assert exc_info.value.error_code == ErrorCode.COMMON_UNAUTHORIZED
diff --git a/test/backend/app/test_northbound_base_app.py b/test/backend/app/test_northbound_base_app.py
index 4316ddd64..56a798916 100644
--- a/test/backend/app/test_northbound_base_app.py
+++ b/test/backend/app/test_northbound_base_app.py
@@ -71,6 +71,27 @@ class SignatureValidationError(Exception):
 # Provide 'consts.exceptions' stub so that northbound_base_app import succeeds
 # ---------------------------------------------------------------------------
 consts_exceptions_module = types.ModuleType("consts.exceptions")
+
+
+class AppException(Exception):
+    """Dummy AppException for testing purposes."""
+    pass
+
+
+class LimitExceededError(Exception):
+    """Dummy rate-limit exception for testing purposes."""
+    pass
+
+class UnauthorizedError(Exception):
+    """Dummy unauthorized exception for testing purposes."""
+    pass
+
+class SignatureValidationError(Exception):
+    """Dummy signature validation exception for testing purposes."""
+    pass
+
+
+consts_exceptions_module.AppException = AppException
 consts_exceptions_module.LimitExceededError = LimitExceededError
 consts_exceptions_module.UnauthorizedError = UnauthorizedError
 consts_exceptions_module.SignatureValidationError = SignatureValidationError
@@ -140,4 +161,4 @@ def test_dummy_endpoint_success(self):
 
 
 if __name__ == "__main__":
-    unittest.main()
\ No newline at end of file
+    unittest.main()
diff --git a/test/backend/consts/test_error_code.py b/test/backend/consts/test_error_code.py
new file mode 100644
index 000000000..11e8aea80
--- /dev/null
+++ b/test/backend/consts/test_error_code.py
@@ -0,0 +1,353 @@
+"""
+Unit tests for Error Code definitions.
+
+Tests the ErrorCode enum and ERROR_CODE_HTTP_STATUS mapping
+to ensure error codes are properly defined and mapped.
+"""
+import pytest
+from backend.consts.error_code import ErrorCode, ERROR_CODE_HTTP_STATUS
+
+
+class TestErrorCodeEnum:
+    """Test class for ErrorCode enum values."""
+
+    def test_dify_error_codes_exist(self):
+        """Test that all Dify-related error codes are defined."""
+        assert ErrorCode.DIFY_SERVICE_ERROR is not None
+        assert ErrorCode.DIFY_CONFIG_INVALID is not None
+        assert ErrorCode.DIFY_CONNECTION_ERROR is not None
+        assert ErrorCode.DIFY_AUTH_ERROR is not None
+        assert ErrorCode.DIFY_RATE_LIMIT is not None
+        assert ErrorCode.DIFY_RESPONSE_ERROR is not None
+
+    def test_datamate_error_codes_exist(self):
+        """Test that DataMate error code is defined."""
+        assert ErrorCode.DATAMATE_CONNECTION_FAILED is not None
+
+    def test_me_error_codes_exist(self):
+        """Test that ME service error code is defined."""
+        assert ErrorCode.ME_CONNECTION_FAILED is not None
+
+
+class TestErrorCodeValues:
+    """Test class for ErrorCode string values with leading zeros."""
+
+    def test_dify_auth_error_value(self):
+        """Test DIFY_AUTH_ERROR has correct string value."""
+        assert ErrorCode.DIFY_AUTH_ERROR.value == "130204"
+
+    def test_dify_config_invalid_value(self):
+        """Test DIFY_CONFIG_INVALID has correct string value."""
+        assert ErrorCode.DIFY_CONFIG_INVALID.value == "130202"
+
+    def test_dify_connection_error_value(self):
+        """Test DIFY_CONNECTION_ERROR has correct string value."""
+        assert ErrorCode.DIFY_CONNECTION_ERROR.value == "130203"
+
+    def test_dify_service_error_value(self):
+        """Test DIFY_SERVICE_ERROR has correct string value."""
+        assert ErrorCode.DIFY_SERVICE_ERROR.value == "130201"
+
+    def test_dify_rate_limit_value(self):
+        """Test DIFY_RATE_LIMIT has correct string value."""
+        assert ErrorCode.DIFY_RATE_LIMIT.value == "130205"
+
+    def test_dify_response_error_value(self):
+        """Test DIFY_RESPONSE_ERROR has correct string value."""
+        assert ErrorCode.DIFY_RESPONSE_ERROR.value == "130206"
+
+    def test_datamate_connection_failed_value(self):
+        """Test DATAMATE_CONNECTION_FAILED has correct string value."""
+        assert ErrorCode.DATAMATE_CONNECTION_FAILED.value == "130101"
+
+    def test_me_connection_failed_value(self):
+        """Test ME_CONNECTION_FAILED has correct string value."""
+        assert ErrorCode.ME_CONNECTION_FAILED.value == "130301"
+
+    def test_common_validation_error_value(self):
+        """Test COMMON_VALIDATION_ERROR has correct string value."""
+        assert ErrorCode.COMMON_VALIDATION_ERROR.value == "000101"
+
+    def test_common_unauthorized_value(self):
+        """Test COMMON_UNAUTHORIZED has correct string value."""
+        assert ErrorCode.COMMON_UNAUTHORIZED.value == "000201"
+
+    def test_common_token_expired_value(self):
+        """Test COMMON_TOKEN_EXPIRED has correct string value."""
+        assert ErrorCode.COMMON_TOKEN_EXPIRED.value == "000203"
+
+    def test_common_token_invalid_value(self):
+        """Test COMMON_TOKEN_INVALID has correct string value."""
+        assert ErrorCode.COMMON_TOKEN_INVALID.value == "000204"
+
+    def test_common_rate_limit_exceeded_value(self):
+        """Test COMMON_RATE_LIMIT_EXCEEDED has correct string value."""
+        assert ErrorCode.COMMON_RATE_LIMIT_EXCEEDED.value == "000302"
+
+    def test_file_not_found_value(self):
+        """Test FILE_NOT_FOUND has correct string value."""
+        assert ErrorCode.FILE_NOT_FOUND.value == "000401"
+
+    def test_file_too_large_value(self):
+        """Test FILE_TOO_LARGE has correct string value."""
+        assert ErrorCode.FILE_TOO_LARGE.value == "000403"
+
+    def test_common_resource_not_found_value(self):
+        """Test COMMON_RESOURCE_NOT_FOUND has correct string value."""
+        assert ErrorCode.COMMON_RESOURCE_NOT_FOUND.value == "000501"
+
+    def test_chat_conversation_not_found_value(self):
+        """Test CHAT_CONVERSATION_NOT_FOUND has correct string value."""
+        assert ErrorCode.CHAT_CONVERSATION_NOT_FOUND.value == "010101"
+
+    def test_knowledge_not_found_value(self):
+        """Test KNOWLEDGE_NOT_FOUND has correct string value."""
+        assert ErrorCode.KNOWLEDGE_NOT_FOUND.value == "060101"
+
+    def test_memory_not_found_value(self):
+        """Test MEMORY_NOT_FOUND has correct string value."""
+        assert ErrorCode.MEMORY_NOT_FOUND.value == "100101"
+
+    def test_model_not_found_value(self):
+        """Test MODEL_NOT_FOUND has correct string value."""
+        assert ErrorCode.MODEL_NOT_FOUND.value == "090101"
+
+    def test_mcp_connection_failed_value(self):
+        """Test MCP_CONNECTION_FAILED has correct string value."""
+        assert ErrorCode.MCP_CONNECTION_FAILED.value == "070201"
+
+    def test_northbound_request_failed_value(self):
+        """Test NORTHBOUND_REQUEST_FAILED has correct string value."""
+        assert ErrorCode.NORTHBOUND_REQUEST_FAILED.value == "140101"
+
+    def test_dataprocess_task_failed_value(self):
+        """Test DATAPROCESS_TASK_FAILED has correct string value."""
+        assert ErrorCode.DATAPROCESS_TASK_FAILED.value == "150101"
+
+    def test_system_unknown_error_value(self):
+        """Test SYSTEM_UNKNOWN_ERROR has correct string value."""
+        assert ErrorCode.SYSTEM_UNKNOWN_ERROR.value == "990101"
+
+    def test_system_internal_error_value(self):
+        """Test SYSTEM_INTERNAL_ERROR has correct string value."""
+        assert ErrorCode.SYSTEM_INTERNAL_ERROR.value == "990105"
+
+
+class TestErrorCodeHttpStatusMapping:
+    """Test class for ERROR_CODE_HTTP_STATUS mapping."""
+
+    def test_dify_auth_error_maps_to_401(self):
+        """Test DIFY_AUTH_ERROR maps to HTTP 401."""
+        assert ERROR_CODE_HTTP_STATUS[ErrorCode.DIFY_AUTH_ERROR] == 401
+
+    def test_dify_config_invalid_maps_to_400(self):
+        """Test DIFY_CONFIG_INVALID maps to HTTP 400."""
+        assert ERROR_CODE_HTTP_STATUS[ErrorCode.DIFY_CONFIG_INVALID] == 400
+
+    def test_dify_connection_error_maps_to_502(self):
+        """Test DIFY_CONNECTION_ERROR maps to HTTP 502."""
+        assert ERROR_CODE_HTTP_STATUS[ErrorCode.DIFY_CONNECTION_ERROR] == 502
+
+    def test_dify_response_error_maps_to_502(self):
+        """Test DIFY_RESPONSE_ERROR maps to HTTP 502."""
+        assert ERROR_CODE_HTTP_STATUS[ErrorCode.DIFY_RESPONSE_ERROR] == 502
+
+    def test_dify_rate_limit_maps_to_429(self):
+        """Test DIFY_RATE_LIMIT maps to HTTP 429."""
+        assert ERROR_CODE_HTTP_STATUS[ErrorCode.DIFY_RATE_LIMIT] == 429
+
+    def test_common_token_expired_maps_to_401(self):
+        """Test COMMON_TOKEN_EXPIRED maps to HTTP 401."""
+        assert ERROR_CODE_HTTP_STATUS[ErrorCode.COMMON_TOKEN_EXPIRED] == 401
+
+    def test_common_token_invalid_maps_to_401(self):
+        """Test COMMON_TOKEN_INVALID maps to HTTP 401."""
+        assert ERROR_CODE_HTTP_STATUS[ErrorCode.COMMON_TOKEN_INVALID] == 401
+
+    def test_common_unauthorized_maps_to_401(self):
+        """Test COMMON_UNAUTHORIZED maps to HTTP 401."""
+        assert ERROR_CODE_HTTP_STATUS[ErrorCode.COMMON_UNAUTHORIZED] == 401
+
+    def test_common_forbidden_maps_to_403(self):
+        """Test COMMON_FORBIDDEN maps to HTTP 403."""
+        assert ERROR_CODE_HTTP_STATUS[ErrorCode.COMMON_FORBIDDEN] == 403
+
+    def test_common_rate_limit_exceeded_maps_to_429(self):
+        """Test COMMON_RATE_LIMIT_EXCEEDED maps to HTTP 429."""
+        assert ERROR_CODE_HTTP_STATUS[ErrorCode.COMMON_RATE_LIMIT_EXCEEDED] == 429
+
+    def test_common_validation_error_maps_to_400(self):
+        """Test COMMON_VALIDATION_ERROR maps to HTTP 400."""
+        assert ERROR_CODE_HTTP_STATUS[ErrorCode.COMMON_VALIDATION_ERROR] == 400
+
+    def test_common_parameter_invalid_maps_to_400(self):
+        """Test COMMON_PARAMETER_INVALID maps to HTTP 400."""
+        assert ERROR_CODE_HTTP_STATUS[ErrorCode.COMMON_PARAMETER_INVALID] == 400
+
+    def test_common_missing_required_field_maps_to_400(self):
+        """Test COMMON_MISSING_REQUIRED_FIELD maps to HTTP 400."""
+        assert ERROR_CODE_HTTP_STATUS[ErrorCode.COMMON_MISSING_REQUIRED_FIELD] == 400
+
+    def test_file_too_large_maps_to_413(self):
+        """Test FILE_TOO_LARGE maps to HTTP 413."""
+        assert ERROR_CODE_HTTP_STATUS[ErrorCode.FILE_TOO_LARGE] == 413
+
+    def test_file_not_found_maps_to_404(self):
+        """Test FILE_NOT_FOUND maps to HTTP 404."""
+        assert ERROR_CODE_HTTP_STATUS[ErrorCode.FILE_NOT_FOUND] == 404
+
+    def test_common_resource_not_found_maps_to_404(self):
+        """Test COMMON_RESOURCE_NOT_FOUND maps to HTTP 404."""
+        assert ERROR_CODE_HTTP_STATUS[ErrorCode.COMMON_RESOURCE_NOT_FOUND] == 404
+
+    def test_common_resource_already_exists_maps_to_409(self):
+        """Test COMMON_RESOURCE_ALREADY_EXISTS maps to HTTP 409."""
+        assert ERROR_CODE_HTTP_STATUS[ErrorCode.COMMON_RESOURCE_ALREADY_EXISTS] == 409
+
+    def test_common_resource_disabled_maps_to_403(self):
+        """Test COMMON_RESOURCE_DISABLED maps to HTTP 403."""
+        assert ERROR_CODE_HTTP_STATUS[ErrorCode.COMMON_RESOURCE_DISABLED] == 403
+
+    def test_system_service_unavailable_maps_to_503(self):
+        """Test SYSTEM_SERVICE_UNAVAILABLE maps to HTTP 503."""
+        assert ERROR_CODE_HTTP_STATUS[ErrorCode.SYSTEM_SERVICE_UNAVAILABLE] == 503
+
+    def test_system_timeout_maps_to_504(self):
+        """Test SYSTEM_TIMEOUT maps to HTTP 504."""
+        assert ERROR_CODE_HTTP_STATUS[ErrorCode.SYSTEM_TIMEOUT] == 504
+
+
+class TestErrorCodeFormat:
+    """Test class for error code format consistency."""
+
+    def test_all_dify_codes_start_with_1302(self):
+        """Test all Dify error codes start with 1302 (module 13, sub-module 02)."""
+        dify_codes = [
+            ErrorCode.DIFY_SERVICE_ERROR,
+            ErrorCode.DIFY_CONFIG_INVALID,
+            ErrorCode.DIFY_CONNECTION_ERROR,
+            ErrorCode.DIFY_AUTH_ERROR,
+            ErrorCode.DIFY_RATE_LIMIT,
+            ErrorCode.DIFY_RESPONSE_ERROR,
+        ]
+        for code in dify_codes:
+            assert str(code.value).startswith("1302"), f"{code} should start with 1302"
+
+    def test_all_datamate_codes_start_with_1301(self):
+        """Test DataMate error code starts with 1301 (module 13, sub-module 01)."""
+        assert str(ErrorCode.DATAMATE_CONNECTION_FAILED.value).startswith("1301")
+
+    def test_all_me_codes_start_with_1303(self):
+        """Test ME service error code starts with 1303 (module 13, sub-module 03)."""
+        assert str(ErrorCode.ME_CONNECTION_FAILED.value).startswith("1303")
+
+    def test_all_common_auth_codes_start_with_0002(self):
+        """Test common auth error codes start with 0002."""
+        auth_codes = [
+            ErrorCode.COMMON_UNAUTHORIZED,
+            ErrorCode.COMMON_TOKEN_EXPIRED,
+            ErrorCode.COMMON_TOKEN_INVALID,
+            ErrorCode.COMMON_FORBIDDEN,
+        ]
+        for code in auth_codes:
+            assert str(code.value).startswith("0002"), f"{code} should start with 0002"
+
+    def test_all_common_validation_codes_start_with_0001(self):
+        """Test common validation error codes start with 0001."""
+        validation_codes = [
+            ErrorCode.COMMON_VALIDATION_ERROR,
+            ErrorCode.COMMON_PARAMETER_INVALID,
+            ErrorCode.COMMON_MISSING_REQUIRED_FIELD,
+        ]
+        for code in validation_codes:
+            assert str(code.value).startswith("0001"), f"{code} should start with 0001"
+
+    def test_all_system_codes_start_with_99(self):
+        """Test system error codes start with 99."""
+        system_codes = [
+            ErrorCode.SYSTEM_UNKNOWN_ERROR,
+            ErrorCode.SYSTEM_SERVICE_UNAVAILABLE,
+            ErrorCode.SYSTEM_DATABASE_ERROR,
+            ErrorCode.SYSTEM_TIMEOUT,
+            ErrorCode.SYSTEM_INTERNAL_ERROR,
+        ]
+        for code in system_codes:
+            assert str(code.value).startswith("99"), f"{code} should start with 99"
+
+    def test_all_chat_codes_start_with_01(self):
+        """Test chat error codes start with 01."""
+        assert str(ErrorCode.CHAT_CONVERSATION_NOT_FOUND.value).startswith("01")
+
+    def test_all_knowledge_codes_start_with_06(self):
+        """Test knowledge error codes start with 06."""
+        assert str(ErrorCode.KNOWLEDGE_NOT_FOUND.value).startswith("06")
+
+    def test_all_mcp_codes_start_with_07(self):
+        """Test MCP error codes start with 07."""
+        assert str(ErrorCode.MCP_CONNECTION_FAILED.value).startswith("07")
+
+    def test_all_model_codes_start_with_09(self):
+        """Test model error codes start with 09."""
+        assert str(ErrorCode.MODEL_NOT_FOUND.value).startswith("09")
+
+    def test_all_memory_codes_start_with_10(self):
+        """Test memory error codes start with 10."""
+        assert str(ErrorCode.MEMORY_NOT_FOUND.value).startswith("10")
+
+    def test_all_northbound_codes_start_with_14(self):
+        """Test northbound error codes start with 14."""
+        assert str(ErrorCode.NORTHBOUND_REQUEST_FAILED.value).startswith("14")
+
+    def test_all_dataprocess_codes_start_with_15(self):
+        """Test dataprocess error codes start with 15."""
+        assert str(ErrorCode.DATAPROCESS_TASK_FAILED.value).startswith("15")
+
+
+class TestErrorCodeStringFormat:
+    """Test that ErrorCode values are strings with 6 digits."""
+
+    def test_error_code_is_string(self):
+        """Test ErrorCode values are strings."""
+        assert isinstance(ErrorCode.DIFY_AUTH_ERROR.value, str)
+        assert ErrorCode.DIFY_AUTH_ERROR.value == "130204"
+
+    def test_error_code_preserves_leading_zeros(self):
+        """Test ErrorCode values preserve leading zeros."""
+        # Common codes have leading zeros
+        assert ErrorCode.COMMON_VALIDATION_ERROR.value == "000101"
+        assert ErrorCode.COMMON_UNAUTHORIZED.value == "000201"
+        assert ErrorCode.COMMON_RATE_LIMIT_EXCEEDED.value == "000302"
+
+    def test_error_code_length_is_six(self):
+        """Test all ErrorCode values have 6 digits."""
+        all_codes = [
+            ErrorCode.COMMON_VALIDATION_ERROR,
+            ErrorCode.COMMON_UNAUTHORIZED,
+            ErrorCode.COMMON_TOKEN_EXPIRED,
+            ErrorCode.DIFY_AUTH_ERROR,
+            ErrorCode.DATAMATE_CONNECTION_FAILED,
+            ErrorCode.CHAT_CONVERSATION_NOT_FOUND,
+            ErrorCode.KNOWLEDGE_NOT_FOUND,
+            ErrorCode.MCP_CONNECTION_FAILED,
+            ErrorCode.SYSTEM_UNKNOWN_ERROR,
+        ]
+        for code in all_codes:
+            assert len(code.value) == 6, f"{code} should have 6 digits"
+
+
+class TestErrorCodeIntConversion:
+    """Test ErrorCode can be converted to integer for JSON response."""
+
+    def test_error_code_can_be_converted_to_int(self):
+        """Test ErrorCode value can be converted to int for HTTP response."""
+        # The response should use int() to convert string to number
+        assert int(ErrorCode.DIFY_AUTH_ERROR.value) == 130204
+        assert int(ErrorCode.COMMON_VALIDATION_ERROR.value) == 101
+
+    def test_error_code_in_conditional(self):
+        """Test ErrorCode can be used in conditionals."""
+        code = ErrorCode.DIFY_AUTH_ERROR
+        if code.value == "130204":
+            assert True
+        else:
+            assert False
diff --git a/test/backend/consts/test_error_message.py b/test/backend/consts/test_error_message.py
new file mode 100644
index 000000000..ae1aa9240
--- /dev/null
+++ b/test/backend/consts/test_error_message.py
@@ -0,0 +1,257 @@
+"""
+Unit tests for Error Message definitions.
+
+Tests the ErrorMessage class and its methods for getting error messages.
+"""
+import pytest
+from backend.consts.error_code import ErrorCode
+from backend.consts.error_message import ErrorMessage
+
+
+class TestErrorMessageGetMessage:
+    """Test class for ErrorMessage.get_message method."""
+
+    def test_get_message_dify_auth_error(self):
+        """Test getting message for DIFY_AUTH_ERROR."""
+        msg = ErrorMessage.get_message(ErrorCode.DIFY_AUTH_ERROR)
+        assert "Dify authentication failed" in msg
+        assert "API key" in msg
+
+    def test_get_message_dify_config_invalid(self):
+        """Test getting message for DIFY_CONFIG_INVALID."""
+        msg = ErrorMessage.get_message(ErrorCode.DIFY_CONFIG_INVALID)
+        assert "Dify configuration" in msg
+
+    def test_get_message_dify_connection_error(self):
+        """Test getting message for DIFY_CONNECTION_ERROR."""
+        msg = ErrorMessage.get_message(ErrorCode.DIFY_CONNECTION_ERROR)
+        assert "connect to Dify" in msg
+
+    def test_get_message_dify_rate_limit(self):
+        """Test getting message for DIFY_RATE_LIMIT."""
+        msg = ErrorMessage.get_message(ErrorCode.DIFY_RATE_LIMIT)
+        assert "rate limit" in msg
+
+    def test_get_message_common_validation_error(self):
+        """Test getting message for COMMON_VALIDATION_ERROR."""
+        msg = ErrorMessage.get_message(ErrorCode.COMMON_VALIDATION_ERROR)
+        assert "Validation" in msg
+
+    def test_get_message_common_unauthorized(self):
+        """Test getting message for COMMON_UNAUTHORIZED."""
+        msg = ErrorMessage.get_message(ErrorCode.COMMON_UNAUTHORIZED)
+        assert "not authorized" in msg.lower()
+
+    def test_get_message_common_token_expired(self):
+        """Test getting message for COMMON_TOKEN_EXPIRED."""
+        msg = ErrorMessage.get_message(ErrorCode.COMMON_TOKEN_EXPIRED)
+        assert "session" in msg.lower()
+        assert "expired" in msg.lower()
+
+    def test_get_message_common_token_invalid(self):
+        """Test getting message for COMMON_TOKEN_INVALID."""
+        msg = ErrorMessage.get_message(ErrorCode.COMMON_TOKEN_INVALID)
+        assert "token" in msg.lower()
+
+    def test_get_message_common_rate_limit_exceeded(self):
+        """Test getting message for COMMON_RATE_LIMIT_EXCEEDED."""
+        msg = ErrorMessage.get_message(ErrorCode.COMMON_RATE_LIMIT_EXCEEDED)
+        assert "requests" in msg.lower()
+
+    def test_get_message_file_not_found(self):
+        """Test getting message for FILE_NOT_FOUND."""
+        msg = ErrorMessage.get_message(ErrorCode.FILE_NOT_FOUND)
+        assert "File" in msg
+        assert "not found" in msg.lower()
+
+    def test_get_message_file_too_large(self):
+        """Test getting message for FILE_TOO_LARGE."""
+        msg = ErrorMessage.get_message(ErrorCode.FILE_TOO_LARGE)
+        assert "size" in msg.lower()
+
+    def test_get_message_system_unknown_error(self):
+        """Test getting message for SYSTEM_UNKNOWN_ERROR."""
+        msg = ErrorMessage.get_message(ErrorCode.SYSTEM_UNKNOWN_ERROR)
+        assert "unknown error" in msg.lower()
+
+    def test_get_message_system_internal_error(self):
+        """Test getting message for SYSTEM_INTERNAL_ERROR."""
+        msg = ErrorMessage.get_message(ErrorCode.SYSTEM_INTERNAL_ERROR)
+        assert "internal" in msg.lower() or "server" in msg.lower()
+
+    def test_get_message_knowledge_not_found(self):
+        """Test getting message for KNOWLEDGE_NOT_FOUND."""
+        msg = ErrorMessage.get_message(ErrorCode.KNOWLEDGE_NOT_FOUND)
+        assert "Knowledge" in msg
+
+    def test_get_message_memory_not_found(self):
+        """Test getting message for MEMORY_NOT_FOUND."""
+        msg = ErrorMessage.get_message(ErrorCode.MEMORY_NOT_FOUND)
+        assert "Memory" in msg
+
+    def test_get_message_mcp_connection_failed(self):
+        """Test getting message for MCP_CONNECTION_FAILED."""
+        msg = ErrorMessage.get_message(ErrorCode.MCP_CONNECTION_FAILED)
+        assert "MCP" in msg
+
+    def test_get_message_northbound_request_failed(self):
+        """Test getting message for NORTHBOUND_REQUEST_FAILED."""
+        msg = ErrorMessage.get_message(ErrorCode.NORTHBOUND_REQUEST_FAILED)
+        assert "Northbound" in msg
+
+    def test_get_message_dataprocess_task_failed(self):
+        """Test getting message for DATAPROCESS_TASK_FAILED."""
+        msg = ErrorMessage.get_message(ErrorCode.DATAPROCESS_TASK_FAILED)
+        assert "Data" in msg or "process" in msg.lower()
+
+    def test_get_message_unknown_code_returns_default(self):
+        """Test that unknown error code returns default message."""
+        # This tests that the fallback works
+        msg = ErrorMessage.get_message(ErrorCode.DIFY_AUTH_ERROR)
+        assert msg != ""
+
+
+class TestErrorMessageGetMessageWithCode:
+    """Test class for ErrorMessage.get_message_with_code method."""
+
+    def test_get_message_with_code_returns_tuple(self):
+        """Test that get_message_with_code returns tuple."""
+        code, msg = ErrorMessage.get_message_with_code(
+            ErrorCode.DIFY_AUTH_ERROR)
+        assert isinstance(code, str)
+        assert isinstance(msg, str)
+
+    def test_get_message_with_code_dify_auth(self):
+        """Test get_message_with_code for DIFY_AUTH_ERROR."""
+        code, msg = ErrorMessage.get_message_with_code(
+            ErrorCode.DIFY_AUTH_ERROR)
+        assert code == "130204"
+        assert "Dify authentication failed" in msg
+
+    def test_get_message_with_code_common_validation(self):
+        """Test get_message_with_code for COMMON_VALIDATION_ERROR."""
+        code, msg = ErrorMessage.get_message_with_code(
+            ErrorCode.COMMON_VALIDATION_ERROR)
+        assert code == "000101"
+        assert "Validation" in msg
+
+    def test_get_message_with_code_system_error(self):
+        """Test get_message_with_code for SYSTEM_INTERNAL_ERROR."""
+        code, msg = ErrorMessage.get_message_with_code(
+            ErrorCode.SYSTEM_INTERNAL_ERROR)
+        assert code == "990105"
+        assert "error" in msg.lower()
+
+    def test_get_message_with_code_tuple_length(self):
+        """Test that get_message_with_code returns exactly 2 elements."""
+        result = ErrorMessage.get_message_with_code(
+            ErrorCode.DIFY_CONFIG_INVALID)
+        assert len(result) == 2
+
+    def test_get_message_with_code_tuple_order(self):
+        """Test that get_message_with_code returns (code, message) in correct order."""
+        code, msg = ErrorMessage.get_message_with_code(
+            ErrorCode.KNOWLEDGE_NOT_FOUND)
+        # First element should be the error code string
+        assert code == ErrorCode.KNOWLEDGE_NOT_FOUND.value
+        # Second element should be the message
+        assert msg == ErrorMessage.get_message(ErrorCode.KNOWLEDGE_NOT_FOUND)
+
+
+class TestErrorMessageGetAllMessages:
+    """Test class for ErrorMessage.get_all_messages method."""
+
+    def test_get_all_messages_returns_dict(self):
+        """Test that get_all_messages returns a dictionary."""
+        messages = ErrorMessage.get_all_messages()
+        assert isinstance(messages, dict)
+
+    def test_get_all_messages_contains_dify_codes(self):
+        """Test that get_all_messages contains Dify error codes."""
+        messages = ErrorMessage.get_all_messages()
+        assert "130201" in messages  # DIFY_SERVICE_ERROR
+        assert "130202" in messages  # DIFY_CONFIG_INVALID
+        assert "130203" in messages  # DIFY_CONNECTION_ERROR
+        assert "130204" in messages  # DIFY_AUTH_ERROR
+        assert "130205" in messages  # DIFY_RATE_LIMIT
+        assert "130206" in messages  # DIFY_RESPONSE_ERROR
+
+    def test_get_all_messages_contains_common_codes(self):
+        """Test that get_all_messages contains common error codes."""
+        messages = ErrorMessage.get_all_messages()
+        assert "000101" in messages  # COMMON_VALIDATION_ERROR
+        assert "000201" in messages  # COMMON_UNAUTHORIZED
+        assert "000203" in messages  # COMMON_TOKEN_EXPIRED
+
+    def test_get_all_messages_contains_system_codes(self):
+        """Test that get_all_messages contains system error codes."""
+        messages = ErrorMessage.get_all_messages()
+        assert "990101" in messages  # SYSTEM_UNKNOWN_ERROR
+        assert "990105" in messages  # SYSTEM_INTERNAL_ERROR
+
+    def test_get_all_messages_all_values_are_strings(self):
+        """Test that all message values in get_all_messages are non-empty strings."""
+        messages = ErrorMessage.get_all_messages()
+        for code, msg in messages.items():
+            assert isinstance(msg, str), f"Message for {code} is not a string"
+            assert len(msg) > 0, f"Message for {code} is empty"
+
+    def test_get_all_messages_all_keys_are_strings(self):
+        """Test that all keys in get_all_messages are string error codes."""
+        messages = ErrorMessage.get_all_messages()
+        for key in messages.keys():
+            assert isinstance(key, str), f"Key {key} is not a string"
+            # Error codes should be numeric strings
+            assert key.isdigit(), f"Key {key} is not a numeric error code"
+
+    def test_get_all_messages_contains_multiple_categories(self):
+        """Test that get_all_messages contains errors from multiple categories."""
+        messages = ErrorMessage.get_all_messages()
+        # Should have errors from different modules
+        # Common (00), Chat (01), Knowledge (06), System (99)
+        has_common = any(key.startswith("00") for key in messages.keys())
+        has_chat = any(key.startswith("01") for key in messages.keys())
+        has_knowledge = any(key.startswith("06") for key in messages.keys())
+        has_system = any(key.startswith("99") for key in messages.keys())
+        assert has_common and has_chat and has_knowledge and has_system
+
+    def test_get_all_messages_count(self):
+        """Test that get_all_messages returns expected number of messages."""
+        messages = ErrorMessage.get_all_messages()
+        # Should have at least 30 error messages
+        assert len(messages) >= 30
+
+    def test_get_all_messages_mcp_codes(self):
+        """Test that get_all_messages contains MCP error codes."""
+        messages = ErrorMessage.get_all_messages()
+        assert "070101" in messages  # MCP_TOOL_NOT_FOUND
+        assert "070102" in messages  # MCP_TOOL_EXECUTION_FAILED
+        assert "070103" in messages  # MCP_TOOL_CONFIG_INVALID
+
+
+class TestErrorMessageCoverage:
+    """Test class for error message coverage."""
+
+    def test_all_error_codes_have_messages(self):
+        """Test that all defined ErrorCodes have messages."""
+        # Get all error codes from ErrorCode enum
+        all_codes = list(ErrorCode)
+
+        for code in all_codes:
+            msg = ErrorMessage.get_message(code)
+            assert msg != "", f"Error code {code} has no message"
+            assert isinstance(msg, str), f"Message for {code} is not a string"
+
+    def test_message_not_generic_for_specific_errors(self):
+        """Test that specific errors have specific messages, not the default."""
+        # Dify auth error should have specific message
+        msg = ErrorMessage.get_message(ErrorCode.DIFY_AUTH_ERROR)
+        assert "authentication failed" in msg.lower()
+
+        # Connection errors should mention connection
+        msg = ErrorMessage.get_message(ErrorCode.DIFY_CONNECTION_ERROR)
+        assert "connect" in msg.lower()
+
+        # Rate limit should mention rate limit
+        msg = ErrorMessage.get_message(ErrorCode.DIFY_RATE_LIMIT)
+        assert "rate" in msg.lower() or "limit" in msg.lower()
diff --git a/test/backend/consts/test_exceptions.py b/test/backend/consts/test_exceptions.py
new file mode 100644
index 000000000..4ec5d0234
--- /dev/null
+++ b/test/backend/consts/test_exceptions.py
@@ -0,0 +1,195 @@
+"""
+Unit tests for Exception classes.
+
+Tests the AppException class and helper functions.
+"""
+import pytest
+from backend.consts.error_code import ErrorCode
+from backend.consts.exceptions import AppException, raise_error
+
+
+class TestAppException:
+    """Test class for AppException."""
+
+    def test_app_exception_creation_with_code(self):
+        """Test creating AppException with error code."""
+        exc = AppException(ErrorCode.DIFY_AUTH_ERROR)
+        assert exc.error_code == ErrorCode.DIFY_AUTH_ERROR
+
+    def test_app_exception_creation_with_custom_message(self):
+        """Test creating AppException with custom message."""
+        custom_msg = "Custom error message"
+        exc = AppException(ErrorCode.DIFY_AUTH_ERROR, custom_msg)
+        assert exc.message == custom_msg
+
+    def test_app_exception_default_message(self):
+        """Test that AppException uses default message when not provided."""
+        exc = AppException(ErrorCode.DIFY_AUTH_ERROR)
+        # Default message should be from ErrorMessage
+        assert exc.message != ""
+        assert "Dify authentication failed" in exc.message
+
+    def test_app_exception_with_details(self):
+        """Test creating AppException with details."""
+        details = {"field": "api_key", "reason": "invalid"}
+        exc = AppException(ErrorCode.DIFY_CONFIG_INVALID, "Invalid config", details)
+        assert exc.details == details
+
+    def test_app_exception_empty_details_defaults_to_dict(self):
+        """Test that empty details defaults to empty dict."""
+        exc = AppException(ErrorCode.DIFY_AUTH_ERROR)
+        assert exc.details == {}
+
+    def test_app_exception_to_dict(self):
+        """Test AppException.to_dict() method."""
+        exc = AppException(ErrorCode.DIFY_AUTH_ERROR, "Auth failed", {"key": "value"})
+        result = exc.to_dict()
+        
+        assert result["code"] == 130204
+        assert result["message"] == "Auth failed"
+        assert result["details"] == {"key": "value"}
+
+    def test_app_exception_to_dict_null_details(self):
+        """Test that to_dict() returns null for empty details."""
+        exc = AppException(ErrorCode.DIFY_AUTH_ERROR, "Auth failed")
+        result = exc.to_dict()
+        
+        assert result["details"] is None
+
+    def test_app_exception_http_status_property(self):
+        """Test AppException.http_status property."""
+        exc = AppException(ErrorCode.DIFY_AUTH_ERROR)
+        assert exc.http_status == 401
+
+    def test_app_exception_http_status_for_different_codes(self):
+        """Test http_status for different error codes."""
+        test_cases = [
+            (ErrorCode.DIFY_AUTH_ERROR, 401),
+            (ErrorCode.DIFY_CONFIG_INVALID, 400),
+            (ErrorCode.DIFY_RATE_LIMIT, 429),
+            (ErrorCode.COMMON_VALIDATION_ERROR, 400),
+            (ErrorCode.COMMON_TOKEN_EXPIRED, 401),
+            (ErrorCode.COMMON_FORBIDDEN, 403),
+        ]
+        
+        for error_code, expected_status in test_cases:
+            exc = AppException(error_code)
+            assert exc.http_status == expected_status, \
+                f"Expected {expected_status} for {error_code}"
+
+    def test_app_exception_is_subclass_of_exception(self):
+        """Test that AppException is a subclass of Exception."""
+        assert issubclass(AppException, Exception)
+
+    def test_app_exception_can_be_raised_and_caught(self):
+        """Test that AppException can be raised and caught."""
+        try:
+            raise AppException(ErrorCode.DIFY_AUTH_ERROR, "Test error")
+        except AppException as e:
+            assert e.error_code == ErrorCode.DIFY_AUTH_ERROR
+            assert e.message == "Test error"
+
+    def test_app_exception_str_representation(self):
+        """Test string representation of AppException."""
+        exc = AppException(ErrorCode.DIFY_AUTH_ERROR, "Test error")
+        assert str(exc) == "Test error"
+
+
+class TestRaiseError:
+    """Test class for raise_error helper function."""
+
+    def test_raise_error_raises_app_exception(self):
+        """Test that raise_error raises AppException."""
+        with pytest.raises(AppException):
+            raise_error(ErrorCode.DIFY_AUTH_ERROR)
+
+    def test_raise_error_with_custom_message(self):
+        """Test raise_error with custom message."""
+        custom_msg = "Custom error"
+        try:
+            raise_error(ErrorCode.DIFY_AUTH_ERROR, custom_msg)
+        except AppException as e:
+            assert e.message == custom_msg
+
+    def test_raise_error_with_details(self):
+        """Test raise_error with details."""
+        details = {"info": "test"}
+        try:
+            raise_error(ErrorCode.DIFY_CONFIG_INVALID, "Error", details)
+        except AppException as e:
+            assert e.details == details
+
+
+class TestLegacyExceptions:
+    """Test class for legacy exception classes."""
+
+    def test_agent_run_exception_exists(self):
+        """Test AgentRunException can be instantiated."""
+        from backend.consts.exceptions import AgentRunException
+        exc = AgentRunException("Agent run failed")
+        assert str(exc) == "Agent run failed"
+
+    def test_limit_exceeded_error_exists(self):
+        """Test LimitExceededError can be instantiated."""
+        from backend.consts.exceptions import LimitExceededError
+        exc = LimitExceededError("Rate limit exceeded")
+        assert str(exc) == "Rate limit exceeded"
+
+    def test_unauthorized_error_exists(self):
+        """Test UnauthorizedError can be instantiated."""
+        from backend.consts.exceptions import UnauthorizedError
+        exc = UnauthorizedError("Unauthorized")
+        assert str(exc) == "Unauthorized"
+
+    def test_validation_error_exists(self):
+        """Test ValidationError can be instantiated."""
+        from backend.consts.exceptions import ValidationError
+        exc = ValidationError("Validation failed")
+        assert str(exc) == "Validation failed"
+
+    def test_not_found_exception_exists(self):
+        """Test NotFoundException can be instantiated."""
+        from backend.consts.exceptions import NotFoundException
+        exc = NotFoundException("Resource not found")
+        assert str(exc) == "Resource not found"
+
+    def test_mcp_connection_error_exists(self):
+        """Test MCPConnectionError can be instantiated."""
+        from backend.consts.exceptions import MCPConnectionError
+        exc = MCPConnectionError("MCP connection failed")
+        assert str(exc) == "MCP connection failed"
+
+    def test_data_mate_connection_error_exists(self):
+        """Test DataMateConnectionError can be instantiated."""
+        from backend.consts.exceptions import DataMateConnectionError
+        exc = DataMateConnectionError("DataMate connection failed")
+        assert str(exc) == "DataMate connection failed"
+
+
+class TestLegacyAliases:
+    """Test class for legacy exception aliases."""
+
+    def test_parameter_invalid_error_alias(self):
+        """Test ParameterInvalidError alias exists."""
+        from backend.consts.exceptions import ParameterInvalidError
+        assert ParameterInvalidError is not None
+
+    def test_timeout_error_alias(self):
+        """Test TimeoutError alias exists."""
+        from backend.consts.exceptions import TimeoutError
+        assert TimeoutError is not None
+
+    def test_user_not_found_error_alias(self):
+        """Test UserNotFoundError alias exists."""
+        from backend.consts.exceptions import UserNotFoundError
+        assert UserNotFoundError is not None
+
+    def test_tenant_not_found_error_alias(self):
+        """Test TenantNotFoundError alias exists."""
+        from backend.consts.exceptions import TenantNotFoundError
+        assert TenantNotFoundError is not None
+
+    def test_agent_not_found_error_alias(self):
+        """Test AgentNotFoundError alias exists."""
+        from backend.consts.exceptions import AgentNotFoundError
+        assert AgentNotFoundError is not None
diff --git a/test/backend/middleware/test_exception_handler.py b/test/backend/middleware/test_exception_handler.py
new file mode 100644
index 000000000..0b2bfc865
--- /dev/null
+++ b/test/backend/middleware/test_exception_handler.py
@@ -0,0 +1,537 @@
+"""
+Unit tests for Exception Handler Middleware.
+
+Tests the ExceptionHandlerMiddleware class and helper functions
+for centralized error handling in the FastAPI application.
+"""
+import atexit
+import sys
+import os
+
+# Add backend directory to path for imports BEFORE any module imports
+# From test/backend/middleware/ -> go up 3 levels to project root -> backend/
+backend_dir = os.path.abspath(os.path.join(
+    os.path.dirname(__file__), "../../../backend"))
+if backend_dir not in sys.path:
+    sys.path.insert(0, backend_dir)
+
+import pytest
+from fastapi import Request, HTTPException
+from fastapi.responses import Response
+from backend.middleware.exception_handler import (
+    ExceptionHandlerMiddleware,
+    _http_status_to_error_code,
+    create_error_response,
+    create_success_response,
+)
+from consts.exceptions import AppException
+from consts.error_code import ErrorCode
+from unittest.mock import patch, MagicMock, AsyncMock, Mock
+
+
+# Apply critical patches before importing any modules
+# This prevents real AWS/MinIO/Elasticsearch calls during import
+patch('botocore.client.BaseClient._make_api_call', return_value={}).start()
+
+# Patch storage factory and MinIO config validation to avoid errors during initialization
+# These patches must be started before any imports that use MinioClient
+storage_client_mock = MagicMock()
+minio_mock = MagicMock()
+minio_mock._ensure_bucket_exists = MagicMock()
+minio_mock.client = MagicMock()
+
+# Start critical patches first - storage factory and config validation must be patched
+# before any module imports that might trigger MinioClient initialization
+critical_patches = [
+    # Patch storage factory and MinIO config validation FIRST
+    patch('nexent.storage.storage_client_factory.create_storage_client_from_config',
+          return_value=storage_client_mock),
+    patch('nexent.storage.minio_config.MinIOStorageConfig.validate',
+          lambda self: None),
+    # Mock boto3 client
+    patch('boto3.client', return_value=Mock()),
+    # Mock boto3 resource
+    patch('boto3.resource', return_value=Mock()),
+    # Mock Elasticsearch to prevent connection errors
+    patch('elasticsearch.Elasticsearch', return_value=Mock()),
+]
+
+for p in critical_patches:
+    p.start()
+
+# Patch MinioClient class to return mock instance when instantiated
+# This prevents real initialization during module import
+patches = [
+    patch('backend.database.client.MinioClient', return_value=minio_mock),
+    patch('database.client.MinioClient', return_value=minio_mock),
+    patch('backend.database.client.minio_client', minio_mock),
+]
+
+for p in patches:
+    p.start()
+
+# Combine all patches for cleanup
+all_patches = critical_patches + patches
+
+# Now safe to import modules that use database.client
+# After import, we can patch get_db_session if needed
+try:
+    from backend.database import client as db_client_module
+    # Patch get_db_session after module is imported
+    db_session_patch = patch.object(
+        db_client_module, 'get_db_session', return_value=Mock())
+    db_session_patch.start()
+    all_patches.append(db_session_patch)
+except ImportError:
+    # If import fails, try patching the path directly (may trigger import)
+    db_session_patch = patch(
+        'backend.database.client.get_db_session', return_value=Mock())
+    db_session_patch.start()
+    all_patches.append(db_session_patch)
+
+# Now safe to import app modules - AFTER all patches are applied
+# Import exception classes
+
+# Import pytest for test decorators
+
+# Stop all patches at the end of the module
+
+
+def stop_patches():
+    for p in all_patches:
+        p.stop()
+
+
+atexit.register(stop_patches)
+
+
+class TestHttpStatusToErrorCode:
+    """Test class for _http_status_to_error_code function."""
+
+    def test_maps_400_to_common_validation_error(self):
+        """Test that HTTP 400 maps to COMMON_VALIDATION_ERROR."""
+        assert _http_status_to_error_code(400) == ErrorCode.COMMON_VALIDATION_ERROR
+
+    def test_maps_401_to_common_unauthorized(self):
+        """Test that HTTP 401 maps to COMMON_UNAUTHORIZED."""
+        assert _http_status_to_error_code(401) == ErrorCode.COMMON_UNAUTHORIZED
+
+    def test_maps_403_to_common_forbidden(self):
+        """Test that HTTP 403 maps to COMMON_FORBIDDEN."""
+        assert _http_status_to_error_code(403) == ErrorCode.COMMON_FORBIDDEN
+
+    def test_maps_404_to_common_resource_not_found(self):
+        """Test that HTTP 404 maps to COMMON_RESOURCE_NOT_FOUND."""
+        assert _http_status_to_error_code(404) == ErrorCode.COMMON_RESOURCE_NOT_FOUND
+
+    def test_maps_429_to_common_rate_limit_exceeded(self):
+        """Test that HTTP 429 maps to COMMON_RATE_LIMIT_EXCEEDED."""
+        assert _http_status_to_error_code(429) == ErrorCode.COMMON_RATE_LIMIT_EXCEEDED
+
+    def test_maps_500_to_system_internal_error(self):
+        """Test that HTTP 500 maps to SYSTEM_INTERNAL_ERROR."""
+        assert _http_status_to_error_code(500) == ErrorCode.SYSTEM_INTERNAL_ERROR
+
+    def test_maps_502_to_system_service_unavailable(self):
+        """Test that HTTP 502 maps to SYSTEM_SERVICE_UNAVAILABLE."""
+        assert _http_status_to_error_code(502) == ErrorCode.SYSTEM_SERVICE_UNAVAILABLE
+
+    def test_maps_503_to_system_service_unavailable(self):
+        """Test that HTTP 503 maps to SYSTEM_SERVICE_UNAVAILABLE."""
+        assert _http_status_to_error_code(503) == ErrorCode.SYSTEM_SERVICE_UNAVAILABLE
+
+    def test_unknown_status_returns_system_unknown_error(self):
+        """Test that unknown HTTP status codes map to SYSTEM_UNKNOWN_ERROR."""
+        assert _http_status_to_error_code(418) == ErrorCode.SYSTEM_UNKNOWN_ERROR
+        assert _http_status_to_error_code(599) == ErrorCode.SYSTEM_UNKNOWN_ERROR
+
+
+class TestCreateErrorResponse:
+    """Test class for create_error_response function."""
+
+    def test_create_error_response_default(self):
+        """Test creating error response with default values."""
+        response = create_error_response(ErrorCode.DIFY_AUTH_ERROR)
+
+        assert response.status_code == 401
+        assert response.body is not None
+
+    def test_create_error_response_custom_message(self):
+        """Test creating error response with custom message."""
+        custom_message = "Custom error message"
+        response = create_error_response(
+            ErrorCode.DIFY_AUTH_ERROR,
+            message=custom_message
+        )
+
+        assert response.status_code == 401
+
+    def test_create_error_response_with_trace_id(self):
+        """Test creating error response with trace ID."""
+        trace_id = "test-trace-id-123"
+        response = create_error_response(
+            ErrorCode.DIFY_AUTH_ERROR,
+            trace_id=trace_id
+        )
+
+        assert response.status_code == 401
+
+    def test_create_error_response_with_details(self):
+        """Test creating error response with additional details."""
+        details = {"field": "api_key", "issue": "invalid format"}
+        response = create_error_response(
+            ErrorCode.DIFY_CONFIG_INVALID,
+            details=details
+        )
+
+        assert response.status_code == 400
+
+    def test_create_error_response_custom_http_status(self):
+        """Test creating error response with custom HTTP status."""
+        response = create_error_response(
+            ErrorCode.DIFY_SERVICE_ERROR,
+            http_status=502
+        )
+
+        assert response.status_code == 502
+
+    def test_create_error_response_dify_auth_error(self):
+        """Test creating error response for DIFY_AUTH_ERROR."""
+        response = create_error_response(ErrorCode.DIFY_AUTH_ERROR)
+
+        assert response.status_code == 401
+
+    def test_create_error_response_dify_config_invalid(self):
+        """Test creating error response for DIFY_CONFIG_INVALID."""
+        response = create_error_response(ErrorCode.DIFY_CONFIG_INVALID)
+
+        assert response.status_code == 400
+
+    def test_create_error_response_dify_rate_limit(self):
+        """Test creating error response for DIFY_RATE_LIMIT."""
+        response = create_error_response(ErrorCode.DIFY_RATE_LIMIT)
+
+        assert response.status_code == 429
+
+    def test_create_error_response_validation_error(self):
+        """Test creating error response for COMMON_VALIDATION_ERROR."""
+        response = create_error_response(ErrorCode.COMMON_VALIDATION_ERROR)
+
+        assert response.status_code == 400
+
+    def test_create_error_response_token_expired(self):
+        """Test creating error response for COMMON_TOKEN_EXPIRED."""
+        response = create_error_response(ErrorCode.COMMON_TOKEN_EXPIRED)
+
+        assert response.status_code == 401
+
+
+class TestCreateSuccessResponse:
+    """Test class for create_success_response function."""
+
+    def test_create_success_response_default(self):
+        """Test creating success response with default values."""
+        response = create_success_response()
+
+        assert response.status_code == 200
+
+    def test_create_success_response_with_data(self):
+        """Test creating success response with data."""
+        data = {"key": "value"}
+        response = create_success_response(data=data)
+
+        assert response.status_code == 200
+
+    def test_create_success_response_custom_message(self):
+        """Test creating success response with custom message."""
+        response = create_success_response(message="Operation successful")
+
+        assert response.status_code == 200
+
+    def test_create_success_response_with_trace_id(self):
+        """Test creating success response with trace ID."""
+        trace_id = "test-trace-id-456"
+        response = create_success_response(trace_id=trace_id)
+
+        assert response.status_code == 200
+
+    def test_create_success_response_all_params(self):
+        """Test creating success response with all parameters."""
+        data = {"result": "ok"}
+        message = "Success"
+        trace_id = "trace-789"
+        response = create_success_response(
+            data=data,
+            message=message,
+            trace_id=trace_id
+        )
+
+        assert response.status_code == 200
+
+
+class TestExceptionHandlerMiddleware:
+    """Test class for ExceptionHandlerMiddleware."""
+
+    @pytest.mark.asyncio
+    async def test_dispatch_normal_request(self):
+        """Test that normal requests pass through without error."""
+        middleware = ExceptionHandlerMiddleware(app=MagicMock())
+
+        mock_request = MagicMock(spec=Request)
+        mock_request.state = MagicMock()
+
+        mock_response = MagicMock(spec=Response)
+        mock_call_next = AsyncMock(return_value=mock_response)
+
+        response = await middleware.dispatch(mock_request, mock_call_next)
+
+        mock_call_next.assert_called_once_with(mock_request)
+        assert response == mock_response
+
+    @pytest.mark.asyncio
+    async def test_dispatch_app_exception(self):
+        """Test handling of AppException."""
+        middleware = ExceptionHandlerMiddleware(app=MagicMock())
+
+        mock_request = MagicMock(spec=Request)
+        mock_request.state = MagicMock()
+
+        # Simulate AppException being raised
+        app_exception = AppException(
+            ErrorCode.DIFY_AUTH_ERROR,
+            "Dify authentication failed"
+        )
+        mock_call_next = AsyncMock(side_effect=app_exception)
+
+        response = await middleware.dispatch(mock_request, mock_call_next)
+
+        assert response.status_code == 401
+
+    @pytest.mark.asyncio
+    async def test_dispatch_http_exception(self):
+        """Test handling of FastAPI HTTPException."""
+        middleware = ExceptionHandlerMiddleware(app=MagicMock())
+
+        mock_request = MagicMock(spec=Request)
+        mock_request.state = MagicMock()
+
+        # Simulate HTTPException being raised
+        http_exception = HTTPException(status_code=404, detail="Not found")
+        mock_call_next = AsyncMock(side_effect=http_exception)
+
+        response = await middleware.dispatch(mock_request, mock_call_next)
+
+        assert response.status_code == 404
+
+    @pytest.mark.asyncio
+    async def test_dispatch_generic_exception(self):
+        """Test handling of generic exceptions."""
+        middleware = ExceptionHandlerMiddleware(app=MagicMock())
+
+        mock_request = MagicMock(spec=Request)
+        mock_request.state = MagicMock()
+
+        # Simulate generic exception being raised
+        generic_exception = RuntimeError("Something went wrong")
+        mock_call_next = AsyncMock(side_effect=generic_exception)
+
+        response = await middleware.dispatch(mock_request, mock_call_next)
+
+        # Should return 500 with internal error code
+        assert response.status_code == 500
+
+    @pytest.mark.asyncio
+    async def test_trace_id_generated(self):
+        """Test that trace ID is generated for each request."""
+        middleware = ExceptionHandlerMiddleware(app=MagicMock())
+
+        mock_request = MagicMock(spec=Request)
+        mock_request.state = MagicMock()
+
+        mock_response = MagicMock(spec=Response)
+        mock_call_next = AsyncMock(return_value=mock_response)
+
+        response = await middleware.dispatch(mock_request, mock_call_next)
+
+        # Verify trace_id was set on request.state
+        assert hasattr(mock_request.state, 'trace_id')
+
+    @pytest.mark.asyncio
+    async def test_app_exception_with_details(self):
+        """Test handling of AppException with details."""
+        middleware = ExceptionHandlerMiddleware(app=MagicMock())
+
+        mock_request = MagicMock(spec=Request)
+        mock_request.state = MagicMock()
+
+        # AppException with details
+        app_exception = AppException(
+            ErrorCode.DIFY_CONFIG_INVALID,
+            "Invalid configuration",
+            details={"field": "api_key"}
+        )
+        mock_call_next = AsyncMock(side_effect=app_exception)
+
+        response = await middleware.dispatch(mock_request, mock_call_next)
+
+        assert response.status_code == 400
+
+    @pytest.mark.asyncio
+    async def test_different_error_codes_map_to_correct_status(self):
+        """Test that different error codes produce correct HTTP status."""
+        test_cases = [
+            (ErrorCode.COMMON_TOKEN_EXPIRED, 401),
+            (ErrorCode.COMMON_TOKEN_INVALID, 401),
+            (ErrorCode.COMMON_FORBIDDEN, 403),
+            (ErrorCode.COMMON_RATE_LIMIT_EXCEEDED, 429),
+            (ErrorCode.COMMON_VALIDATION_ERROR, 400),
+            (ErrorCode.FILE_TOO_LARGE, 413),
+        ]
+
+        middleware = ExceptionHandlerMiddleware(app=MagicMock())
+        mock_request = MagicMock(spec=Request)
+        mock_request.state = MagicMock()
+
+        for error_code, expected_status in test_cases:
+            app_exception = AppException(error_code, "Test error")
+            mock_call_next = AsyncMock(side_effect=app_exception)
+
+            response = await middleware.dispatch(mock_request, mock_call_next)
+
+            assert response.status_code == expected_status, \
+                f"Expected {expected_status} for {error_code}, got {response.status_code}"
+
+
+class TestErrorResponseFormat:
+    """Test class for error response format."""
+
+    def test_error_response_contains_code_as_int(self):
+        """Test that error response contains code as integer."""
+        response = create_error_response(ErrorCode.DIFY_AUTH_ERROR)
+        # Parse response body
+        import json
+        body = json.loads(response.body)
+        assert "code" in body
+        # Code should be integer when converted (string "130204" -> int 130204)
+        assert body["code"] == 130204
+
+    def test_error_response_contains_message(self):
+        """Test that error response contains message."""
+        response = create_error_response(ErrorCode.DIFY_AUTH_ERROR, message="Custom message")
+        import json
+        body = json.loads(response.body)
+        assert body["message"] == "Custom message"
+
+    def test_error_response_contains_trace_id(self):
+        """Test that error response contains trace_id."""
+        response = create_error_response(ErrorCode.DIFY_AUTH_ERROR, trace_id="test-123")
+        import json
+        body = json.loads(response.body)
+        assert body["trace_id"] == "test-123"
+
+    def test_error_response_contains_details(self):
+        """Test that error response contains details."""
+        details = {"field": "api_key", "reason": "invalid"}
+        response = create_error_response(ErrorCode.DIFY_CONFIG_INVALID, details=details)
+        import json
+        body = json.loads(response.body)
+        assert body["details"] == details
+
+    def test_error_response_details_null_when_not_provided(self):
+        """Test that details is null when not provided."""
+        response = create_error_response(ErrorCode.DIFY_AUTH_ERROR)
+        import json
+        body = json.loads(response.body)
+        assert body["details"] is None
+
+
+class TestNewErrorCodes:
+    """Test class for new error codes."""
+
+    def test_datamate_connection_failed(self):
+        """Test DATAMATE_CONNECTION_FAILED error code."""
+        assert ErrorCode.DATAMATE_CONNECTION_FAILED.value == "130101"
+
+    def test_me_connection_failed(self):
+        """Test ME_CONNECTION_FAILED error code."""
+        assert ErrorCode.ME_CONNECTION_FAILED.value == "130301"
+
+    def test_northbound_request_failed(self):
+        """Test NORTHBOUND_REQUEST_FAILED error code."""
+        assert ErrorCode.NORTHBOUND_REQUEST_FAILED.value == "140101"
+
+    def test_northbound_config_invalid(self):
+        """Test NORTHBOUND_CONFIG_INVALID error code."""
+        assert ErrorCode.NORTHBOUND_CONFIG_INVALID.value == "140201"
+
+    def test_dataprocess_task_failed(self):
+        """Test DATAPROCESS_TASK_FAILED error code."""
+        assert ErrorCode.DATAPROCESS_TASK_FAILED.value == "150101"
+
+    def test_dataprocess_parse_failed(self):
+        """Test DATAPROCESS_PARSE_FAILED error code."""
+        assert ErrorCode.DATAPROCESS_PARSE_FAILED.value == "150102"
+
+    def test_quick_config_invalid(self):
+        """Test QUICK_CONFIG_INVALID error code."""
+        assert ErrorCode.QUICK_CONFIG_INVALID.value == "020101"
+
+    def test_agentspace_agent_not_found(self):
+        """Test AGENTSPACE_AGENT_NOT_FOUND error code."""
+        assert ErrorCode.AGENTSPACE_AGENT_NOT_FOUND.value == "030101"
+
+    def test_knowledge_not_found(self):
+        """Test KNOWLEDGE_NOT_FOUND error code."""
+        assert ErrorCode.KNOWLEDGE_NOT_FOUND.value == "060101"
+
+    def test_memory_not_found(self):
+        """Test MEMORY_NOT_FOUND error code."""
+        assert ErrorCode.MEMORY_NOT_FOUND.value == "100101"
+
+    def test_profile_user_not_found(self):
+        """Test PROFILE_USER_NOT_FOUND error code."""
+        assert ErrorCode.PROFILE_USER_NOT_FOUND.value == "110101"
+
+    def test_tenant_not_found(self):
+        """Test TENANT_NOT_FOUND error code."""
+        assert ErrorCode.TENANT_NOT_FOUND.value == "120101"
+
+    def test_mcp_tool_not_found(self):
+        """Test MCP_TOOL_NOT_FOUND error code."""
+        assert ErrorCode.MCP_TOOL_NOT_FOUND.value == "070101"
+
+    def test_mcp_name_illegal(self):
+        """Test MCP_NAME_ILLEGAL error code."""
+        assert ErrorCode.MCP_NAME_ILLEGAL.value == "070301"
+
+    def test_model_not_found(self):
+        """Test MODEL_NOT_FOUND error code."""
+        assert ErrorCode.MODEL_NOT_FOUND.value == "090101"
+
+
+class TestAppExceptionToDict:
+    """Test class for AppException.to_dict() method."""
+
+    def test_to_dict_contains_code(self):
+        """Test that to_dict contains code as integer."""
+        exc = AppException(ErrorCode.DIFY_AUTH_ERROR, "Auth failed")
+        result = exc.to_dict()
+        assert result["code"] == 130204
+
+    def test_to_dict_contains_message(self):
+        """Test that to_dict contains message."""
+        exc = AppException(ErrorCode.DIFY_AUTH_ERROR, "Custom message")
+        result = exc.to_dict()
+        assert result["message"] == "Custom message"
+
+    def test_to_dict_contains_details(self):
+        """Test that to_dict contains details."""
+        exc = AppException(ErrorCode.DIFY_CONFIG_INVALID, "Invalid", details={"key": "value"})
+        result = exc.to_dict()
+        assert result["details"] == {"key": "value"}
+
+    def test_to_dict_details_null_when_empty(self):
+        """Test that details is null when empty dict."""
+        exc = AppException(ErrorCode.DIFY_AUTH_ERROR, "Auth failed", details={})
+        result = exc.to_dict()
+        assert result["details"] is None
diff --git a/test/backend/services/test_dify_service.py b/test/backend/services/test_dify_service.py
index a6ed3b091..77090711f 100644
--- a/test/backend/services/test_dify_service.py
+++ b/test/backend/services/test_dify_service.py
@@ -9,6 +9,9 @@
 from unittest.mock import MagicMock, patch
 import httpx
 
+from backend.consts.error_code import ErrorCode
+from backend.consts.exceptions import AppException
+
 
 def _create_mock_client(mock_response):
     """
@@ -145,82 +148,84 @@ def test_fetch_dify_datasets_impl_empty_response(self):
         assert result["pagination"]["embedding_available"] is False
 
     def test_fetch_dify_datasets_impl_invalid_api_base_none(self):
-        """Test ValueError when dify_api_base is None."""
+        """Test AppException when dify_api_base is None."""
         from backend.services.dify_service import fetch_dify_datasets_impl
 
-        with pytest.raises(ValueError) as excinfo:
+        # Catch Exception and verify it's an AppException with expected error code
+        with pytest.raises(Exception) as excinfo:
             fetch_dify_datasets_impl(
                 dify_api_base=None,
                 api_key="test-api-key"
             )
 
-        assert "dify_api_base is required and must be a non-empty string" in str(
-            excinfo.value)
+        # Verify it's an AppException with the correct error code
+        assert hasattr(excinfo.value, 'error_code')
+        assert excinfo.value.error_code.value == ErrorCode.DIFY_CONFIG_INVALID.value
 
     def test_fetch_dify_datasets_impl_invalid_api_base_empty_string(self):
-        """Test ValueError when dify_api_base is empty string."""
+        """Test AppException when dify_api_base is empty string."""
         from backend.services.dify_service import fetch_dify_datasets_impl
 
-        with pytest.raises(ValueError) as excinfo:
+        with pytest.raises(Exception) as excinfo:
             fetch_dify_datasets_impl(
                 dify_api_base="",
                 api_key="test-api-key"
             )
 
-        assert "dify_api_base is required and must be a non-empty string" in str(
-            excinfo.value)
+        assert hasattr(excinfo.value, 'error_code')
+        assert excinfo.value.error_code.value == ErrorCode.DIFY_CONFIG_INVALID.value
 
     def test_fetch_dify_datasets_impl_invalid_api_base_not_string(self):
-        """Test ValueError when dify_api_base is not a string."""
+        """Test AppException when dify_api_base is not a string."""
         from backend.services.dify_service import fetch_dify_datasets_impl
 
-        with pytest.raises(ValueError) as excinfo:
+        with pytest.raises(Exception) as excinfo:
             fetch_dify_datasets_impl(
                 dify_api_base=12345,
                 api_key="test-api-key"
             )
 
-        assert "dify_api_base is required and must be a non-empty string" in str(
-            excinfo.value)
+        assert hasattr(excinfo.value, 'error_code')
+        assert excinfo.value.error_code.value == ErrorCode.DIFY_CONFIG_INVALID.value
 
     def test_fetch_dify_datasets_impl_invalid_api_key_none(self):
-        """Test ValueError when api_key is None."""
+        """Test AppException when api_key is None."""
         from backend.services.dify_service import fetch_dify_datasets_impl
 
-        with pytest.raises(ValueError) as excinfo:
+        with pytest.raises(Exception) as excinfo:
             fetch_dify_datasets_impl(
                 dify_api_base="https://dify.example.com",
                 api_key=None
             )
 
-        assert "api_key is required and must be a non-empty string" in str(
-            excinfo.value)
+        assert hasattr(excinfo.value, 'error_code')
+        assert excinfo.value.error_code.value == ErrorCode.DIFY_CONFIG_INVALID.value
 
     def test_fetch_dify_datasets_impl_invalid_api_key_empty_string(self):
-        """Test ValueError when api_key is empty string."""
+        """Test AppException when api_key is empty string."""
         from backend.services.dify_service import fetch_dify_datasets_impl
 
-        with pytest.raises(ValueError) as excinfo:
+        with pytest.raises(Exception) as excinfo:
             fetch_dify_datasets_impl(
                 dify_api_base="https://dify.example.com",
                 api_key=""
             )
 
-        assert "api_key is required and must be a non-empty string" in str(
-            excinfo.value)
+        assert hasattr(excinfo.value, 'error_code')
+        assert excinfo.value.error_code.value == ErrorCode.DIFY_CONFIG_INVALID.value
 
     def test_fetch_dify_datasets_impl_invalid_api_key_not_string(self):
-        """Test ValueError when api_key is not a string."""
+        """Test AppException when api_key is not a string."""
         from backend.services.dify_service import fetch_dify_datasets_impl
 
-        with pytest.raises(ValueError) as excinfo:
+        with pytest.raises(Exception) as excinfo:
             fetch_dify_datasets_impl(
                 dify_api_base="https://dify.example.com",
                 api_key=[]  # list is not a string
             )
 
-        assert "api_key is required and must be a non-empty string" in str(
-            excinfo.value)
+        assert hasattr(excinfo.value, 'error_code')
+        assert excinfo.value.error_code.value == ErrorCode.DIFY_CONFIG_INVALID.value
 
     def test_fetch_dify_datasets_impl_url_normalization_trailing_slash(self):
         """Test that trailing slash is removed from API base URL."""
@@ -695,3 +700,154 @@ def test_fetch_dify_datasets_impl_url_v1_suffix_parametrized(self, api_base_url)
         assert "/v1/v1" not in called_url, f"URL duplication detected: {called_url}"
         # Verify URL ends with /v1/datasets
         assert called_url.endswith("/v1/datasets")
+
+    def test_fetch_dify_datasets_impl_url_without_protocol(self):
+        """Test ValueError when dify_api_base doesn't start with http:// or https://."""
+        from backend.services.dify_service import fetch_dify_datasets_impl
+
+        with pytest.raises(Exception) as excinfo:
+            fetch_dify_datasets_impl(
+                dify_api_base="dify.example.com",
+                api_key="test-api-key"
+            )
+
+        assert "must start with http:// or https://" in str(excinfo.value)
+
+    def test_fetch_dify_datasets_impl_url_with_ftp_protocol(self):
+        """Test ValueError when dify_api_base uses unsupported protocol."""
+        from backend.services.dify_service import fetch_dify_datasets_impl
+
+        with pytest.raises(Exception) as excinfo:
+            fetch_dify_datasets_impl(
+                dify_api_base="ftp://dify.example.com",
+                api_key="test-api-key"
+            )
+
+        assert "must start with http:// or https://" in str(excinfo.value)
+
+    def test_fetch_dify_datasets_impl_http_401_auth_error(self):
+        """Test that HTTP 401 maps to DIFY_AUTH_ERROR."""
+        mock_response = MagicMock()
+        # Create a proper mock response object with status_code as a real integer
+        mock_response.raise_for_status.side_effect = httpx.HTTPStatusError(
+            "401 Unauthorized",
+            request=MagicMock(),
+            response=type('MockResponse', (), {'status_code': 401})()
+        )
+
+        mock_client = _create_mock_client(mock_response)
+
+        with patch('backend.services.dify_service.http_client_manager') as mock_manager:
+            mock_manager.get_sync_client.return_value = mock_client
+
+            from backend.services.dify_service import fetch_dify_datasets_impl
+
+            # Catch Exception and verify it's an AppException with DIFY_AUTH_ERROR
+            with pytest.raises(Exception) as excinfo:
+                fetch_dify_datasets_impl(
+                    dify_api_base="https://dify.example.com",
+                    api_key="test-api-key"
+                )
+
+            assert hasattr(excinfo.value, 'error_code')
+            assert excinfo.value.error_code.value == ErrorCode.DIFY_AUTH_ERROR.value
+
+    def test_fetch_dify_datasets_impl_http_403_auth_error(self):
+        """Test that HTTP 403 maps to DIFY_AUTH_ERROR."""
+        mock_response = MagicMock()
+        mock_response.raise_for_status.side_effect = httpx.HTTPStatusError(
+            "403 Forbidden",
+            request=MagicMock(),
+            response=type('MockResponse', (), {'status_code': 403})()
+        )
+
+        mock_client = _create_mock_client(mock_response)
+
+        with patch('backend.services.dify_service.http_client_manager') as mock_manager:
+            mock_manager.get_sync_client.return_value = mock_client
+
+            from backend.services.dify_service import fetch_dify_datasets_impl
+
+            with pytest.raises(Exception) as excinfo:
+                fetch_dify_datasets_impl(
+                    dify_api_base="https://dify.example.com",
+                    api_key="test-api-key"
+                )
+
+            assert hasattr(excinfo.value, 'error_code')
+            assert excinfo.value.error_code.value == ErrorCode.DIFY_AUTH_ERROR.value
+
+    def test_fetch_dify_datasets_impl_http_429_rate_limit(self):
+        """Test that HTTP 429 maps to DIFY_RATE_LIMIT."""
+        mock_response = MagicMock()
+        mock_response.raise_for_status.side_effect = httpx.HTTPStatusError(
+            "429 Too Many Requests",
+            request=MagicMock(),
+            response=type('MockResponse', (), {'status_code': 429})()
+        )
+
+        mock_client = _create_mock_client(mock_response)
+
+        with patch('backend.services.dify_service.http_client_manager') as mock_manager:
+            mock_manager.get_sync_client.return_value = mock_client
+
+            from backend.services.dify_service import fetch_dify_datasets_impl
+
+            with pytest.raises(Exception) as excinfo:
+                fetch_dify_datasets_impl(
+                    dify_api_base="https://dify.example.com",
+                    api_key="test-api-key"
+                )
+
+            assert hasattr(excinfo.value, 'error_code')
+            assert excinfo.value.error_code.value == ErrorCode.DIFY_RATE_LIMIT.value
+
+    def test_fetch_dify_datasets_impl_http_500_service_error(self):
+        """Test that HTTP 500 maps to DIFY_SERVICE_ERROR."""
+        mock_response = MagicMock()
+        mock_response.raise_for_status.side_effect = httpx.HTTPStatusError(
+            "500 Internal Server Error",
+            request=MagicMock(),
+            response=type('MockResponse', (), {'status_code': 500})()
+        )
+
+        mock_client = _create_mock_client(mock_response)
+
+        with patch('backend.services.dify_service.http_client_manager') as mock_manager:
+            mock_manager.get_sync_client.return_value = mock_client
+
+            from backend.services.dify_service import fetch_dify_datasets_impl
+
+            with pytest.raises(Exception) as excinfo:
+                fetch_dify_datasets_impl(
+                    dify_api_base="https://dify.example.com",
+                    api_key="test-api-key"
+                )
+
+            assert hasattr(excinfo.value, 'error_code')
+            assert excinfo.value.error_code.value == ErrorCode.DIFY_SERVICE_ERROR.value
+
+    def test_fetch_dify_datasets_impl_http_404_service_error(self):
+        """Test that HTTP 404 maps to DIFY_SERVICE_ERROR."""
+        mock_response = MagicMock()
+        mock_response.raise_for_status.side_effect = httpx.HTTPStatusError(
+            "404 Not Found",
+            request=MagicMock(),
+            response=type('MockResponse', (), {'status_code': 404})()
+        )
+
+        mock_client = _create_mock_client(mock_response)
+
+        with patch('backend.services.dify_service.http_client_manager') as mock_manager:
+            mock_manager.get_sync_client.return_value = mock_client
+
+            from backend.services.dify_service import fetch_dify_datasets_impl
+
+            with pytest.raises(Exception) as excinfo:
+                fetch_dify_datasets_impl(
+                    dify_api_base="https://dify.example.com",
+                    api_key="test-api-key"
+                )
+
+            assert hasattr(excinfo.value, 'error_code')
+            assert excinfo.value.error_code.value == ErrorCode.DIFY_SERVICE_ERROR.value