ROB-003: Unknown methods get -32601 Method not found

Severity	Applies to	Spec section
error	both eras, stdio, http	2026-07-28/basic/transports/streamable-http#protocol-version-header

Calls a method no server implements (mcpprobe/no-such-method). On Streamable HTTP in the 2026-07-28 era the server MUST respond with 404 Not Found and a JSON-RPC error with code -32601. On stdio, and in initialize-era sessions, every request MUST get a response under JSON-RPC 2.0 (https://modelcontextprotocol.io/specification/2026-07-28/basic/index#messages), and -32601 is the code JSON-RPC defines for a method that does not exist; the error must echo the request id. Runs once per server.

From the command line: mcpprobe checks explain ROB-003. To leave it out of a run, add "ROB-003" to [checks] disable in mcpprobe.toml; to change how much it counts, use severity_overrides.