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The session writes OTEL spans to JSONL; mcp-eval converts them to rich metrics:
- Tool calls (names, args, times, errors)
- Iteration count, response latency
- Token and cost estimates
- Tool coverage by server (available vs used)
Sources:
Span tree analysis
SpanTree enables:
- LLM rephrasing loop detection
- Inefficient tool paths analysis
- Error recovery sequences
Artifacts
- Traces:
./test-reports/*.jsonl
- Per‑test JSON results:
./test-reports/*_results.json
- Combined JSON/Markdown/HTML (via runner options)