mcp-server

Implement server/discover, carry protocol version and client capabilities in each request's _meta envelope, and use Streamable HTTP or stdio as the transport. There is no initialize handshake or session header; cross-call state becomes a server-minted handle passed as a tool argument.

Writing anything to stdout that is not a JSON-RPC frame corrupts the protocol stream. A write without a trailing newline prefixes the next frame, the client loses that response, and the call times out. Route all logging to stderr.

@modelcontextprotocol/sdk is the retired v1 single package ending at 1.30.0. The v2 line ships as scoped packages (@modelcontextprotocol/core, @modelcontextprotocol/server) at 2.0.0, and migration is a dependency change aided by the official codemod.

Validate the token's audience against your server's canonical URI on every request, never forward the inbound token to upstream APIs, and request the narrowest scopes needed. Return 401 with WWW-Authenticate for invalid tokens and 403 with a scope challenge for insufficient scope.

Thrown exceptions are handled inconsistently: mcp 2.2.0 discards the message while TypeScript SDKs forward it verbatim, secrets included. Catch exceptions in the handler and return a result with isError: true plus text naming the next recovery action.

It does not cover operating someone else's published server, writing agent skills, general language idioms, container deployment, or full-codebase security audits. Those belong to operator tasks, the skill-authoring, language, cloud, and security-review skills respectively.