fastapi-mcp-router 0.3.0

Lightweight FastAPI integration for Model Context Protocol (MCP)

fastapi-mcp-router

Add MCP to your existing FastAPI app. Register tools, resources, and prompts with decorators. Use Depends(), Request, and BackgroundTasks the same way you already do.

Why fastapi-mcp-router

• It's just an APIRouter. Mount it like any other router. No separate framework, no new server process.
• Your DI still works. Depends(), Request, BackgroundTasks — same patterns, same middleware.
• 2 dependencies. FastAPI and Pydantic. Nothing else.
• No lock-in. Tools are regular async functions. Call them from tests, CLI scripts, or other endpoints without MCP.
• Lambda-ready. Stateless mode + Mangum. No adapter layer.

Use FastMCP instead if you need STDIO transport, OpenAPI spec imports, or managed hosting.

Install

pip install fastapi-mcp-router

Quick Start

from fastapi import FastAPI
from fastapi_mcp_router import MCPRouter

app = FastAPI()
mcp = MCPRouter()

@mcp.tool()
async def write_message(payload: str) -> dict:
    """Write coordination message."""
    return {"success": True, "message_id": "msg-123"}

@mcp.resource("project://{project_id}/config")
async def project_config(project_id: str) -> dict:
    return {"project_id": project_id, "env": "production"}

@mcp.prompt()
async def review_code(file_path: str, language: str = "python") -> list[dict]:
    return [{"role": "user", "content": f"Review {file_path} ({language})"}]

app.include_router(mcp, prefix="/mcp")

That's it. Your FastAPI app now speaks MCP over Streamable HTTP.

What You Get

• Full MCP 2025-06-18 spec — tools, resources, prompts, sampling, logging, completions, elicitation
• Streamable HTTP — JSON or SSE response based on Accept header
• Streaming tools — return AsyncGenerator for incremental results
• Session management — in-memory and Redis stores for stateful connections
• Progress reporting — inject ProgressCallback into tool signatures
• Auth — auth_validator callback + OAuth 2.1 PRM (RFC 9728)
• OpenTelemetry — opt-in spans and counters via pip install fastapi-mcp-router[otel]
• Lambda-ready — stateless mode works with Mangum, no adapter overhead

Documentation

• Quick Start — installation, first tool, stateful mode, auth, Lambda
• Guide — resources, prompts, streaming, sessions, telemetry
• API Reference — all exports, types, and configuration options

License

MIT