LangGraph A2A Client

A2A (Agent-to-Agent) Protocol Client Tool for LangGraph.

Overview

This library provides functionality to discover and communicate with A2A-compliant agents in LangGraph applications.

Key Features

• Agent discovery through agent cards from multiple URLs
• Message sending to specific A2A agents
• LangChain tool integration for easy use in LangGraph workflows

Installation

pip install langgraph-a2a-client

Or with uv:

uv add langgraph-a2a-client

Usage

from langgraph_a2a_client import A2AClientToolProvider

# Initialize the A2A client
a2a_client = A2AClientToolProvider(
    known_agent_urls=["https://example.com/agent"],
    timeout=300,
    webhook_url="https://your-webhook.com/notify",
    webhook_token="your-webhook-token",
    headers={
        "https://example.com/agent": {"X-API-Key": "your-api-key"}
    }  # Optional: Per-URL headers for authentication
)

# Get the tools for use in LangGraph
tools = a2a_client.tools

# Use in your LangGraph application
# ...

API

A2AClientToolProvider

Main class that provides A2A client functionality.

Parameters

• known_agent_urls (list[str] | None): List of A2A agent URLs to discover initially
• timeout (int): Timeout for HTTP operations in seconds (default: 300)
• webhook_url (str | None): Optional webhook URL for push notifications
• webhook_token (str | None): Optional authentication token for webhook notifications
• headers (dict[str, dict[str, str]] | None): Optional per-URL HTTP headers for authentication. Format: {"https://agent-url.com": {"X-API-Key": "key", "Authorization": "Bearer token"}}

Tools

The provider exposes three tools:

1. a2a_discover_agent: Discover an A2A agent and return its agent card
2. a2a_list_discovered_agents: List all discovered A2A agents and their capabilities
3. a2a_send_message: Send a message to a specific A2A agent

Authentication

The client supports configuring HTTP headers per agent URL for authentication:

API Key Authentication (Per URL)

a2a_client = A2AClientToolProvider(
    known_agent_urls=["https://agent1.example.com", "https://agent2.example.com"],
    headers={
        "https://agent1.example.com": {"X-API-Key": "api-key-for-agent1"},
        "https://agent2.example.com": {"X-API-Key": "api-key-for-agent2"}
    }
)

Bearer Token Authentication

a2a_client = A2AClientToolProvider(
    known_agent_urls=["https://example.com/agent"],
    headers={
        "https://example.com/agent": {"Authorization": "Bearer your-token"}
    }
)

Custom Headers (Per URL)

a2a_client = A2AClientToolProvider(
    known_agent_urls=["https://example.com/agent"],
    headers={
        "https://example.com/agent": {
            "X-Custom-Header": "custom-value",
            "X-Client-ID": "client-123",
            "Authorization": "Bearer token"
        }
    }
)

Multiple Agents with Different Authentication

a2a_client = A2AClientToolProvider(
    known_agent_urls=[
        "https://public-agent.example.com",
        "https://secure-agent.example.com"
    ],
    headers={
        # Secure agent requires authentication
        "https://secure-agent.example.com": {
            "X-API-Key": "secret-key",
            "X-Tenant-ID": "tenant-123"
        }
        # Public agent has no entry, so no headers are added
    }
)

Examples

Basic Usage

uv run examples/basic_usage.py

Authentication Usage

uv run examples/authentication_usage.py

Supervisor Agent Example

export OPENAI_API_KEY="your-openai-api"
uv run --extra examples examples/supervisor_agent.py

License

MIT