The Model Context Protocol lets you build servers that expose data and functionality to LLM applications in a secure, standardized way. Think of it like a web API, but designed for LLM interactions. With this SDK you can:
Build MCP servers that expose tools, resources, and prompts to any MCP host
Build MCP clients that connect to any MCP server
Speak every standard transport: stdio, Streamable HTTP, and SSE
Requirements
Python 3.11+.
Installation
uv add "mcp[cli]" # or: pip install "mcp[cli]"
The cli extra adds the mcp command-line tool (mcp dev, mcp run, mcp install) on top of the SDK; install plain mcp if you don't need it. For one-off commands, uv run --with "mcp[cli]" mcp ... works without a project.
A server in 15 lines
Create a server.py:
from mcp.server import MCPServer
mcp = MCPServer("Demo")
@mcp.tool()
def add(a: int, b: int) -> int:
"""Add two numbers."""
return a + b
@mcp.resource("greeting://{name}")
def greeting(name: str) -> str:
"""Greet someone by name."""
return f"Hello, {name}!"
That's a complete MCP server: one tool, one templated resource. Open it in the MCP Inspector:
uv run mcp dev server.py
Call add with a=1, b=2 and you get 3 back.
Notice what you did not write: no JSON Schema (a: int, b: intis the schema), no request parsing, no validation code, no protocol handling. Two type-hinted Python functions and a docstring.
The same package is a full MCP client. Serve server.py over HTTP:
uv run mcp run server.py --transport streamable-http
then point a Client at it:
import asyncio
from mcp import Client
async def main() -> None:
async with Client("http://localhost:8000/mcp") as client:
result = await client.call_tool("add", {"a": 1, "b": 2})
print(result.structured_content) # {'result': 3}
asyncio.run(main())
A URL means Streamable HTTP, the transport you deploy. Client can also launch a local server as a stdio subprocess or take any custom transport; Clients has the rest.
Contributing
We are passionate about supporting contributors of all levels of experience and would love to see you get involved in the project. See the contributing guide to get started.
License
This project is licensed under the MIT License. See the LICENSE file for details.
