Failure modes

A failure mode is a recurring, nameable way an agent goes wrong. Common ones: hallucinated facts, wrong tool selection, malformed tool arguments, context lost mid-conversation, loops that never terminate, tasks declared done that were not, instructions overridden by retrieved content.

Failure modes exist because agent failures share causes. A given prompt, retrieval setup, or tool interface produces the same class of error across many different inputs, so failures that look unrelated in isolation often turn out to be the same mode with the same cause.

Naming a mode makes it measurable. Once a failure mode has a name, it's concrete enough to write a grader for, count, and track over time. A mode observed at a specific rate is a measurement, and a set of modes with rates describes an agent's reliability precisely enough to compare across versions.

Which modes dominate depends on the architecture, because each architecture creates its own opportunities to fail. RAG agents fail at grounding, tool-heavy agents fail at argument formation, and multi-agent systems fail at handoffs. The distribution across modes is usually skewed, with a small number of modes accounting for most observed failures.