MCP standardizes how an AI client (Claude, Cursor, an agent framework) talks to an MCP server that exposes tools, resources and prompts. Messages use JSON-RPC 2.0 over a transport (today streamable HTTP for remote servers, or stdio locally).
The ecosystem passed 5,800+ community servers in the official registry, with Google and Microsoft shipping their own agent registries — making MCP one of the fastest-growing developer ecosystems of the AI era.
The handshake and message format between an AI client and a tool server: initialize, capability negotiation, and how tools/resources/prompts are listed and called — so any compliant client can use any compliant server.