Max Isbey
0875dbb926
The merge window landed the listen server runtime, the client response cache, requestState integrity, stream-pair 2026 serving, and the client extension API — invalidating the premises of ~45 deferral texts and notes written against the older base. Each text now states what is true at this pin: entries whose blocking surface landed flip to 'Not yet covered here' naming what a test will drive; entries still blocked name the precise missing surface. Also fixes the README era-lock line (stateless is locked too), documents the default-on client cache in the transport-matrix section, and renames one resource test whose name predated its retarget.
MCP Python SDK
Python implementation of the Model Context Protocol (MCP)
Note
This is v2 of the MCP Python SDK, the current stable release line. It is a major rework of the SDK, both to support the 2026-07-28 MCP specification (and every earlier revision) and to fix long-standing architectural issues. Coming from v1? See What's new in v2 for the tour of what changed and the migration guide for every breaking change.
Not ready to migrate? v1.x lives on the
v1.xbranch, continues to receive critical bug fixes and security patches, and is documented at https://py.sdk.modelcontextprotocol.io/v1/. Sincepip install mcpnow installs 2.x, keep a<2upper bound on your requirement (for examplemcp>=1.28,<2) until you've migrated.Something rough, confusing, or broken? Open an issue or find us in #python-sdk-dev on the MCP Contributors Discord.
Documentation
The documentation lives at https://py.sdk.modelcontextprotocol.io/.
It has a Get started guide, What's new in v2, the API reference, and the migration guide.
What is MCP?
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 3.10+.
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}!"
Full example: docs_src/index/tutorial001.py
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: int is the schema), no request parsing, no validation code, no protocol handling. Two type-hinted Python functions and a docstring.
Get started takes it from here.
A client in 10 lines
The same package is a full MCP client. Client connects to a URL, a stdio subprocess, a custom transport, or (for tests) straight to a server object in memory with no transport at all:
import asyncio
from mcp import Client
from server import mcp
async def main() -> None:
async with Client(mcp) as client:
result = await client.call_tool("add", {"a": 1, "b": 2})
print(result.structured_content) # {'result': 3}
asyncio.run(main())
Swap mcp for "http://localhost:8000/mcp" and the exact same code talks to a remote server.
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.