ROB-002: Invalid JSON-RPC envelopes are rejected, not executed

Severity	Applies to	Spec section
warn	both eras, stdio, http	2026-07-28/basic/index#requests

Sends four messages that are valid JSON but not valid MCP requests: no "jsonrpc" member, "jsonrpc": "1.0", a method that is a number, and a JSON array holding one request (MCP has no batching since 2025-06-18, so it is not sent in a 2025-03-26 session; on Streamable HTTP the body MUST be a single request or notification, https://modelcontextprotocol.io/specification/2026-07-28/basic/transports/streamable-http#sending-messages). Each should get a JSON-RPC error, ideally -32600 (Invalid Request), or on HTTP a 4xx status. Fails if one is executed (a result) or gets no answer. A warning, because JSON-RPC 2.0 shows these answers in examples rather than MUSTs; a crash or hang fails the run regardless. Runs once per server, as one case that reports the first failing message and how many failed.

From the command line: mcpprobe checks explain ROB-002. To leave it out of a run, add "ROB-002" to [checks] disable in mcpprobe.toml; to change how much it counts, use severity_overrides.