CONF-015: stdio: stdout carries only newline-delimited JSON-RPC messages¶
| Severity | Applies to | Spec section |
|---|---|---|
| error | both eras, stdio | 2026-07-28/basic/transports/stdio#stdio |
Inspects every line the server wrote to stdout during the suite. The server MUST NOT write anything to stdout that is not a valid MCP message, and messages are newline-delimited. Logging belongs on stderr. 2025-11-25 states the same rules (https://modelcontextprotocol.io/specification/2025-11-25/basic/transports#stdio). On servers that speak both eras it runs twice: once with modern requests, and once inside a legacy initialize session as
From the command line: mcpprobe checks explain CONF-015. To leave it out of a run, add "CONF-015" to [checks] disable in mcpprobe.toml; to change how much it counts, use severity_overrides.