Trace Analysis for Multi-Step Failures

In a multi-step pipeline, the final visible symptom is often several hops downstream of the actual fault. Fixing the symptom without finding the earliest deviation just relocates the bug.

What Trace Analysis Is

Use trace analysis -- logs of every call, tool invocation, retrieval hit, and result -- to find the earliest deviation, not just the final symptom. A wrong final answer might trace back to a bad retrieval hit three steps earlier, a tool call that returned stale data, or a prompt instruction that was misread early in the chain.

Why the Earliest Deviation Matters

If you only look at the final output, you diagnose the symptom where it became visible, not where it originated. Two different root causes (a retrieval problem vs. a prompt problem) can produce the same-looking final symptom; only the trace -- the sequence of intermediate calls and results -- distinguishes them.

Relationship to Production Monitoring

Trace analysis is the diagnostic counterpart to production logging: the same request/response, tool-call, and retrieval logs captured for live monitoring are what you replay to find the earliest deviation during a diagnostic pass. Without that logging in place beforehand, there is no trace to analyze after the fact.

Common exam traps

• Misclassifying the failure type. A well-formed but factually invented output is a hallucination -- not a transport error, not truncation, and not automatically a model-mismatch regression. Trace analysis is what lets you confirm which one actually occurred rather than guessing from the symptom alone.