MCP Server Frameworks & SDKs — FastMCP, Official SDKs, and the Tools That Power Every MCP Server

Every MCP server is built on something. Behind the 5,000+ servers in the ecosystem, a surprisingly small number of frameworks and SDKs do the heavy lifting — handling JSON-RPC transport, tool schema generation, authentication, and the protocol handshake that makes MCP work. This review covers the tools developers use to build MCP servers: official SDKs maintained by the Agentic AI Foundation (donated by Anthropic in late 2025), and the third-party frameworks that add higher-level abstractions on top. The ecosystem spans five languages — Python , TypeScript , Go , Java , and Kotlin — with Python dominating adoption by a wide margin. Rating: 4.5/5. The headline: FastMCP is the most important project in the MCP ecosystem that most users never see. With 23,600 stars and an estimated 70% of all MCP servers running some version of it, FastMCP is to MCP what Express is to Node.js — the framework that made the protocol accessible. Python — The Dominant Ecosystem FastMCP (PrefectHQ) — 23,600 st