FastMCP is a standard framework for building Model Context Protocol (MCP) applications, which connect LLMs to tools and data. It simplifies the process by automatically generating schemas, validation, and documentation for tools, and managing transport negotiation and authentication for server connections. FastMCP offers a comprehensive solution for developing, deploying, and scaling MCP-powered systems.

Is fastmcp open source?

Yes, licensed under Apache-2.0.

fastmcp

Active·★ 28.0k·Apache-2.0·Updated 2026-10-08

★ Most Popular★ Dev Tooling★ LLM Infra

FastMCP, built by the team at Prefect, is a Python framework for MCP servers, clients and interactive apps. You declare a tool as an ordinary Python function and FastMCP generates the schema, validation and documentation; you connect to a server with a URL and it handles transport negotiation. FastMCP 1.0 was incorporated into the official MCP Python SDK in 2024, and the standalone project continues as the actively developed framework.

It is the natural choice for Python developers who want to expose internal APIs, databases or scripts to AI assistants, build MCP clients to test or orchestrate servers, or add interactive UIs to tools with FastMCP Apps. A TypeScript counterpart, FastMCP for TypeScript, is maintained by the same team. Documentation is extensive and also published in llms.txt format so coding agents can read it.

Getting started: add it to a project with `uv add fastmcp`, write a function decorated with `@mcp.tool`, and call `mcp.run()`. Upgrade guides cover migrations from earlier FastMCP versions and from the official SDK.

#agents#fastmcp#llms#mcp#mcp-clients#mcp-servers#mcp-tools#model-context-protocol

Features

01Automatic schema, validation, and documentation generation for tools

02Managed transport negotiation, authentication, and protocol lifecycle for server connections

03Wraps Python functions into MCP-compliant tools, resources, and prompts (Servers)

04Connects to any MCP server with full protocol support (Clients)

05Provides interactive UIs for tools rendered directly in conversations (Apps)

Why choose it

+Very little boilerplate: schemas and validation are generated from type hints and docstrings.

+Covers servers, clients and interactive apps in one framework, with an official TypeScript sibling.

+Mature and widely used, with thorough documentation and migration guides.

+Apache-2.0 licensed.

Trade-offs

!Major versions have introduced breaking changes, so pin versions and read the upgrade guides when moving between them.

!Enterprise features such as a private registry, SSO and tool-level access control are part of Prefect's commercial Horizon product rather than the open-source framework.

!Python-focused; TypeScript users need the separate FastMCP for TypeScript project.

Compatibility

Python

Python Library

Verified via docs

Quick start

$ uv add fastmcp

Use cases

↳Building LLM applications that interact with custom tools and data sources

↳Creating interactive conversational UIs for backend functionalities

↳Developing and deploying scalable MCP servers and clients

How it compares

≈vs the official MCP Python SDK: the SDK includes the original FastMCP 1.0 interface; the standalone FastMCP adds clients, apps and a faster release cadence.

≈vs FastMCP (TypeScript, by punkpeye): a separate community framework with a similar name for building MCP servers in TypeScript; Prefect's official TypeScript counterpart is FastMCP for TypeScript.

≈vs MCP SDKs for other languages: if your service is written in C#, Java, Kotlin, Rust or PHP, the official SDKs for those languages may integrate more naturally.

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