Python MCP SDK: Complete Developer Guide

Overview

The Python MCP SDK is the official library for building MCP servers in Python. It supports tools, resources, prompts, transports, and the stdio and streamable-http transport.

Installation

pip install mcp

Minimal Server Example

from mcp.server.fastmcp import FastMCP

mcp = FastMCP("my-server")

@mcp.tool()
def add(a: int, b: int) -> int:
    """Add two numbers."""
    return a + b

if __name__ == "__main__":
    mcp.run(transport="stdio")

Adding a Tool

Tools are the primary way MCP servers expose functionality to clients. Each tool has a name, input schema, and handler function.

@mcp.tool()
async def get_weather(city: str) -> dict:
    """Get weather for a city."""
    return await fetch_weather(city)

Supported Features

Testing Your Server

1. Start the server and verify it prints no startup errors.
2. Run npx @modelcontextprotocol/inspector and connect over stdio.
3. Call your tools and verify they return the expected responses.
4. Connect from Claude Desktop and confirm tool visibility.