diff --git a/src/raglite/_rag.py b/src/raglite/_rag.py
index 25fc2bd4..ecef7f67 100644
--- a/src/raglite/_rag.py
+++ b/src/raglite/_rag.py
@@ -2,6 +2,8 @@
 
 import json
 from collections.abc import AsyncIterator, Callable, Iterator
+from concurrent.futures import ThreadPoolExecutor, as_completed
+from functools import partial
 from typing import Any
 
 import numpy as np
@@ -141,35 +143,56 @@ def _get_tools(
     return tools, tool_choice
 
 
+def _run_tool(
+    tool_call: ChatCompletionMessageToolCall,
+    on_retrieval: Callable[[list[ChunkSpan]], None] | None,
+    config: RAGLiteConfig,
+) -> dict[str, Any]:
+    """Run a single tool to search the knowledge base for RAG context."""
+    if tool_call.function.name == "search_knowledge_base":
+        kwargs = json.loads(tool_call.function.arguments)
+        kwargs["config"] = config
+        chunk_spans = retrieve_context(**kwargs)
+        message = {
+            "role": "tool",
+            "content": '{{"documents": [{elements}]}}'.format(
+                elements=", ".join(
+                    chunk_span.to_json(index=i + 1) for i, chunk_span in enumerate(chunk_spans)
+                )
+            ),
+            "tool_call_id": tool_call.id,
+        }
+
+        if chunk_spans and callable(on_retrieval):
+            on_retrieval(chunk_spans)
+    else:
+        error_message = f"Unknown function `{tool_call.function.name}`."
+        raise ValueError(error_message)
+    return message
+
+
 def _run_tools(
     tool_calls: list[ChatCompletionMessageToolCall],
     on_retrieval: Callable[[list[ChunkSpan]], None] | None,
     config: RAGLiteConfig,
+    max_workers: int | None = None,
 ) -> list[dict[str, Any]]:
     """Run tools to search the knowledge base for RAG context."""
-    tool_messages: list[dict[str, Any]] = []
-    for tool_call in tool_calls:
-        if tool_call.function.name == "search_knowledge_base":
-            kwargs = json.loads(tool_call.function.arguments)
-            kwargs["config"] = config
-            chunk_spans = retrieve_context(**kwargs)
-            tool_messages.append(
-                {
-                    "role": "tool",
-                    "content": '{{"documents": [{elements}]}}'.format(
-                        elements=", ".join(
-                            chunk_span.to_json(index=i + 1)
-                            for i, chunk_span in enumerate(chunk_spans)
-                        )
-                    ),
-                    "tool_call_id": tool_call.id,
-                }
-            )
-            if chunk_spans and callable(on_retrieval):
-                on_retrieval(chunk_spans)
-        else:
-            error_message = f"Unknown function `{tool_call.function.name}`."
-            raise ValueError(error_message)
+    tool_messages: list[dict[str, Any]] = [None] * len(tool_calls)  # type: ignore[list-item]
+    with ThreadPoolExecutor(max_workers=max_workers) as executor:
+        futures = [
+            executor.submit(partial(_run_tool, tool_call, on_retrieval, config))
+            for tool_call in tool_calls
+        ]
+        future_to_index = {future: i for i, future in enumerate(futures)}
+        for future in as_completed(futures):
+            try:
+                message = future.result()
+                tool_messages[future_to_index[future]] = message
+            except Exception as e:  # noqa: PERF203
+                executor.shutdown(cancel_futures=True)  # Cancel remaining work.
+                error_message = f"Error executing tool: {e}"
+                raise ValueError(error_message) from e
     return tool_messages