FastMCP

FastMCP is the standard Python framework for building Model Context Protocol (MCP) applications — servers, clients, and interactive apps. A plain Python function decorated with @mcp.tool becomes an MCP tool with auto-generated JSON Schema, validation, and documentation; transports (stdio, Streamable HTTP), auth, and protocol lifecycle are handled by the framework.

Verified live 2026-10-13: the project now lives at PrefectHQ/fastmcp (moved from jlowin/fastmcp at v3.0.0, Feb 2026; the old URL redirects), maintained by the Prefect team, with 28,052 stars, Apache-2.0 license, and docs at gofastmcp.com. FastMCP 1.0 was incorporated into the official Anthropic MCP Python SDK in 2024 — independently corroborated by third-party architecture decision records (serpeter/diatagma ADR-001 documents choosing FastMCP 3.x over the official SDK). Three pillars: Servers (tools, resources, prompts), Clients (any MCP server, programmatic or CLI), and Apps (interactive UIs rendered inside the conversation). Notable production features: OAuth/OIDC auth, server composition and proxying, OpenAPI/FastAPI import, middleware, lifespan management, elicitation, sampling, OpenTelemetry, and a CLI that installs servers into Claude Desktop/Code, Cursor, ChatGPT, Gemini CLI, and Goose.

1. Add to your project: uv add fastmcp (or pip install fastmcp), Python 3.10+.
2. Write a server — minimal example:

```python

from fastmcp import FastMCP

mcp = FastMCP("Demo")

@mcp.tool

def add(a: int, b: int) -> int:

"""Add two numbers"""

return a + b

if __name__ == "__main__":

mcp.run()

```

1. Run it: fastmcp run server.py (stdio for local clients, or Streamable HTTP for remote).
2. Install into a client: fastmcp install server.py wires it into Claude Desktop/Code, Cursor, etc.
3. Full walkthrough: https://gofastmcp.com/getting-started/quickstart (upgrade guides exist for v2 → v3 and SDK v1 → v2).