FastMCP

Decorating a Python function is all it takes to expose a tool over the Model Context Protocol with FastMCP, whose 1.0 release was absorbed into the official MCP Python SDK; the actively developed v2 goes well beyond the spec basics. Servers gain authentication, server composition, and proxying, an OpenAPI or FastAPI application can be converted into an MCP server automatically, and the framework covers clients too, with in-memory testing utilities, sampling, elicitation, and a CLI for running and inspecting servers. Created by Prefect founder Jeremiah Lowin and maintained with Prefect's backing, it has become the default way Python developers build MCP integrations, reflected in roughly 27,000 GitHub stars and wide adoption across the agent ecosystem. Installation is a single pip or uv command, servers run over stdio or HTTP, and everything works offline since MCP servers need no model access of their own. The framework is Apache-2.0 licensed, with FastMCP Cloud available as a hosted deployment option forming the commercial tier.