FastMCP

FastMCP is Prefect's open-source Python framework for building Model Context Protocol (MCP) servers and clients. It helps developers expose functions, data, and reusable prompts to AI applications. Your code defines the behavior; the framework handles schemas, validation, and protocol communication.

Key Highlights

• Python decorators turn functions into MCP tools.
• Resources and prompts expose data and reusable instructions.
• Client library connects to local and remote MCP servers.
• FastAPI and OpenAPI integration can generate MCP interfaces.
• CLI runs servers locally or over HTTP.

What Makes It Different

FastMCP builds tool schemas from Python functions, so developers can work with familiar code instead of assembling protocol messages. It combines server authoring and client connections in one framework. The official TypeScript counterpart is built and maintained by the same team at Prefect.

Features & Capabilities

Install with uv add fastmcp or pip install fastmcp, create a FastMCP instance, and register functions with @mcp.tool. Start a saved server with fastmcp run server.py. The default stdio transport suits local client connections; Streamable HTTP serves clients over the network.

For existing APIs, generate MCP components from an OpenAPI definition or FastAPI app, or mount an MCP server inside FastAPI. Treat automatic API conversion as a starting point for prototyping: choose tools around agent tasks rather than exposing every endpoint. FastAPI must be installed separately.

User Ratings and Testimonials

Evaluate FastMCP by connecting your intended client and checking tool schemas, results, and error handling. A concrete maintenance tradeoff is version compatibility: minor releases can include breaking changes. Pin exact dependencies and test upgrades before deploying them.

Pricing & Value

• Open-source framework: Free to use and self-host under the Apache 2.0 license. Local execution and your own infrastructure are supported.
• Prefect Horizon: A separate enterprise offering for managed hosting and governance. Its hosted services, SSO, and tool-level RBAC are separate from the free framework.

For teams that want to write and run their own MCP tools, the framework provides the Python application layer without a software subscription.