FastAPI-MCP

0.4.0 · active · verified Wed Apr 01

FastAPI-MCP is a Python library that automatically converts FastAPI endpoints into Model Context Protocol (MCP) tools, enabling seamless integration with Large Language Models (LLMs) and AI agents. It provides a straightforward way to expose existing FastAPI APIs as discoverable and callable tools for AI. The library is currently at version 0.4.0 and maintains an active release cadence with frequent updates and feature additions.

Warnings

breaking The `mount()` method is deprecated as of v0.4.0 and will be removed in future versions. It previously handled SSE transport by default.
Fix: Use `mcp.mount_http()` for HTTP transport (recommended) or `mcp.mount_sse()` for Server-Sent Events (SSE) transport instead.
breaking The `base_url` argument was removed from the `FastApiMCP` constructor. It is now redundant due to the default use of ASGI transport.
Fix: Remove the `base_url` argument when initializing `FastApiMCP`. If an explicit base URL is required, configure it via the `http_client` argument with your own `httpx.AsyncClient`.
breaking Version 0.2.0 introduced a complete refactor from a function-based API to a new class-based `FastApiMCP` API. This changed how MCP instances are created and mounted.
Fix: Migrate your code to use the `FastApiMCP` class (e.g., `mcp = FastApiMCP(app)` followed by `mcp.mount()`, or `mcp.mount_http()`/`mcp.mount_sse()` in later versions).
gotcha FastAPI-MCP uses the `operation_id` from your FastAPI routes as the MCP tool names. If `operation_id` is not explicitly provided, FastAPI auto-generates a cryptic one.
Fix: Always provide an explicit `operation_id` parameter to your FastAPI route definitions (`@app.get('/path', operation_id='my_tool_name')`) for clearer and more intuitive tool names for AI agents.
gotcha FastAPI-MCP depends on the `mcp` package. Breaking changes in the `mcp` SDK itself (e.g., `mcp` SDK 1.8.0) can cause issues with `fastapi-mcp` if not explicitly handled.
Fix: Ensure your `mcp` dependency is compatible with your `fastapi-mcp` version. Refer to `fastapi-mcp` release notes for required `mcp` versions (e.g., v0.3.4 fixed an issue by upgrading `mcp` to 1.8.1).

Install

pip install fastapi-mcp uvicorn Install with pip
uv add fastapi-mcp uvicorn Install with uv

Imports

FastApiMCP
```
from fastapi_mcp import FastApiMCP
```
Ensure you import from `fastapi_mcp` for the FastAPI integration, not the generic `fastmcp` SDK.

Quickstart

This quickstart demonstrates how to create a basic FastAPI application, instantiate `FastApiMCP` with your app, and then mount the MCP server using the recommended `mount_http()` method. The `operation_id` is explicitly set for clarity in the exposed MCP tool. To run, save as `main.py` and execute `python main.py`. The MCP server will be available at `http://localhost:8000/mcp`.

from fastapi import FastAPI
from fastapi_mcp import FastApiMCP

# Create a FastAPI app
app = FastAPI(title="My MCP API")

@app.get("/hello")
def read_root():
    return {"message": "Hello, World!"}

@app.get("/items/{item_id}", operation_id="get_item_by_id")
def read_item(item_id: int):
    """Get a specific item by its ID"""
    return {"item_id": item_id, "name": f"Item {item_id}"}

# Create an MCP server based on this app
mcp = FastApiMCP(app)

# Mount the MCP server to your app using the recommended HTTP transport
mcp.mount_http()

if __name__ == "__main__":
    import uvicorn
    uvicorn.run(app, host="0.0.0.0", port=8000)

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