MCP Builder

Build interoperable MCP implementations against the stable 2026-07-28 specification. Treat extensions as negotiated, opt-in capabilities rather than core protocol guarantees.

1. Stable baseline and compatibility

• The authoritative stable baseline is MCP 2026-07-28.
• Core requests are stateless and self-contained. Do not infer protocol version, client capabilities, identity, conversation, or task state from a transport connection or process lifetime.
• Put cross-request state behind explicit identifiers supplied on every relevant request.
• Negotiate the protocol version and capabilities; do not assume that a client or server implements every optional feature.
• Preserve compatibility with earlier peers where the specification requires it, including accepting legacy resource-not-found error code -32002 while emitting -32602 for invalid parameters in the current protocol.

Core versus extensions