When an agent system fails in production — and given enough time, every agent system fails in production — it almost always fails in one of three ways. It loops forever, burning tokens and accomplishing nothing. Or its plan was wrong from the start and every well-executed step takes it further from the goal. Or its tool calls did real damage, because the tool surface was wider than the trust model warranted. The good news: each failure mode has a known root cause, and each root cause has a known engineering fix. This field guide is the diagnostic manual.
Companion to the Scaling Agentic AI and Production Playbook series. Those documents argue for verification as the missing architectural piece; this one is the failure taxonomy that motivates the argument.
What it covers
Three failure modes plus a checklist, about eleven minutes.
§ 1 — Failure 1: the infinite loop. Symptom: token cost climbs without progress. Root cause: the agent has no termination condition that the verifier actually enforces. Fix: explicit loop budgets, progress-checking verifiers, the did the state change check before the next iteration.
§ 2 — Failure 2: the broken plan. Symptom: every step is correctly executed and the result is wrong. Root cause: the plan was built before the agent had enough context; subsequent execution doesn’t notice the plan is failing. Fix: re-planning checkpoints, evidence-driven plan revision, the is this plan still working check between sub-tasks.
§ 3 — Failure 3: unsafe tool use. Symptom: the agent does real harm — leaks secrets, mass-deletes data, sends bad emails. Root cause: the tool surface was wider than the principle of least privilege. Fix: scoped tool calls, mandatory human-in-the-loop confirmation for irreversible actions, the minimum capability needed for the task discipline.
§ 4 — The diagnostic checklist. Twelve symptoms grouped by failure mode. When you see this in your logs, look here in your code.
Read it
The field guide lives at its own URL with a warm-paper layout — fault-red accent for symptoms, verify-green accent for fixes. Diagnostic manual format throughout.
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