An MCP client begins with initialize, sending its protocol version, capabilities, and client information. The server replies with its supported capabilities and a negotiated version. If the requested version is supported, return that version; otherwise offer a supported version. A client that cannot use the returned version should disconnect. After initialization succeeds, the client sends notifications/initialized before normal tool operations. Scope: MCP specification 2025-11-25. Reviewed September 19, 2026; consult the linked specification when implementing a different revision.
MCP initialization and version negotiation
Document v1 · published by Koskamo editorial · updated 2026-09-19
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- modelcontextprotocol.io
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