Max Isbey
6b0166f3d1
OAuthClientInformationFull, the client's parse of the authorization server's Dynamic Client Registration response, inherited from OAuthClientMetadata, the request the client sends. That typed the response as though it had to be a request this SDK would send. RFC 7591 3.2.1 says otherwise: the server may reject or replace any requested metadata value, and real servers echo an application_type outside OIDC Registration's web/native, an explicit null, an auth method the SDK does not implement, or an empty redirect_uris. Each raised ValidationError on a 2xx response, after the server had already provisioned the client, so the registration was discarded and orphaned. Make the two models siblings over a shared OAuthClientMetadataBase. The request keeps its strict types, so the SDK still refuses to send an unregistered application_type. The record accepts what a server may echo: application_type and token_endpoint_auth_method are str | None (with an echoed "" read as absent, as the optional URL fields already were), grant_types is list[str], and redirect_uris may be absent or empty. client_id is now required, as RFC 7591 3.2.1 makes it in the response. Whether a substituted value is usable is judged where it matters, not at parse: an auth method the client cannot apply is reported as an OAuthRegistrationError when the registration completes, before the record is stored or any interactive authorization begins, and prepare_token_auth reports the same for a stored record. The recognized set is derived from the one TokenEndpointAuthMethod type so the two cannot drift. The bundled registration endpoint now returns all registered metadata in its 201 response, building the record from the validated request's dump so a field can no longer be silently dropped from the echo; it previously omitted application_type, reporting the default in place of a client's "web".
MCP Python SDK
Python implementation of the Model Context Protocol (MCP)
Caution
This README documents v2 of the MCP Python SDK — a pre-release (alpha/beta) line under active development. Do not use v2 in production. Pre-releases are published to PyPI as
2.0.0aN/2.0.0bN, and each pre-release may contain breaking changes from the previous one. Pin an exact version and expect to update your code when you bump the pin.v1.x is the only stable release line and remains recommended for production. It lives on the
v1.xbranch and continues to receive critical bug fixes and security patches; see the v1.x README for its documentation.pipanduvdon't select a pre-release unless you explicitly request one, so existing installs are unaffected. If your package depends onmcp, add a<2upper bound to your version constraint (for examplemcp>=1.27,<2) before the stable release lands.v2 is a major rework of the SDK, both to support the 2026-07-28 MCP specification release and to fix long-standing architectural issues. See What's new in v2 for the tour of what changed, and the migration guide for every breaking change. Stable v2 is targeted for 2026-07-28, alongside the spec release. Try the pre-releases and tell us what breaks, or discuss in #python-sdk-dev on the MCP Contributors Discord.
Documentation
The documentation lives at https://py.sdk.modelcontextprotocol.io/v2/.
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]==2.0.0b1" # or: pip install "mcp[cli]==2.0.0b1"
The pin matters while v2 is in pre-release: an unpinned install resolves to the latest stable v1.x, which this README does not describe. Check PyPI for the newest pre-release, and use uv run --with "mcp==2.0.0b1" for one-off commands.
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.