ROB-001: Malformed JSON gets a -32700 Parse error

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

Sends a request cut off in the middle of its JSON. All MCP messages MUST follow JSON-RPC 2.0, which answers unparsable input with error -32700 (Parse error) and id null. On Streamable HTTP a 4xx status is accepted too, with or without a JSON-RPC body. A warning, not an error: JSON-RPC 2.0 shows this answer in its examples rather than requiring it in a MUST, and many SDKs log the bad line and answer nothing. A server that crashes or stops answering after the input fails the run regardless, through the liveness probe that follows every case. Runs once per server.

From the command line: mcpprobe checks explain ROB-001. To leave it out of a run, add "ROB-001" to [checks] disable in mcpprobe.toml; to change how much it counts, use severity_overrides.