Troubleshooting
The command does not start
Section titled “The command does not start”Confirm Node.js 22.19.0 or newer is active, then check the published CLI:
node --versionnpx mcp-failure-lab --helpserve appears silent
Section titled “serve appears silent”That is expected. The stdio server waits for an MCP client and keeps stdout clean for protocol messages. Connect with MCP Inspector or another stdio-capable client.
A scenario times out unexpectedly
Section titled “A scenario times out unexpectedly”Check the scenario’s timeoutMs against the requested delay. When omitted, the CLI uses 30 seconds for each primary or observer call.
Result text does not match
Section titled “Result text does not match”textContains is case-sensitive and inspects only MCP content items with type text. It does not search arbitrary serialized result fields.
The observer failed after disconnect
Section titled “The observer failed after disconnect”Observer calls reuse the same MCP client connection. Because disconnect closes that transport, the observer cannot verify state afterward.
JSON output is not valid
Section titled “JSON output is not valid”Use --report json. If you are integrating the stdio server directly, ensure your own diagnostics do not mix with protocol traffic on stdout.
Exit code 2
Section titled “Exit code 2”Execution completed, but at least one expectation failed. Exit code 1 instead means the scenario could not be loaded or executed.