The AI agent failure encyclopedia

Autonomous agents fail in recognizable, repeatable ways. This is the catalog Snapback diagnoses against — each class grounded in the MAST and TRAIL research taxonomies.

planning coordination

Loop Repeated Tool Call

Agent repeats the same/near-same tool call without progress. MAST 'step repetition' (specification/design); TRAIL resour…

system execution

Unhandled Tool Error

A tool returned an error the agent didn't handle. Primarily TRAIL system-execution. Includes cryptic agent-INFRASTRUCTUR…

reasoning

Hallucinated Tool Args

Agent invented/incorrect tool arguments. TRAIL reasoning (hallucination) + execution.

system execution

Tool Schema

A tool/protocol call failed on its SCHEMA or FORMAT — wrong request shape, wrong network/scheme identifier, a protocol-l…

reasoning

Missing Information Gathering

Agent acted without gathering needed info. Both taxonomies touch this via context/clarify.

planning coordination

Wrong Tool Selection

Chose an inappropriate tool for the goal.

reasoning

Incorrect Reasoning

Flawed reasoning led to the failure. Core TRAIL reasoning category.

reasoning

Incorrect Code

Generated code was wrong. Neither taxonomy has a dedicated code class; maps to reasoning.

system execution

Cost Blowout

Excessive spend/tokens. MAST does not formalize cost; TRAIL 'resource abuse' is closest. Snapback treats operational cos…

reasoning

Context Overflow

Context window exceeded / history lost. Direct MAST 'loss of history'.

system execution

Timeout Step Limit

Hit a step/time limit before completing.

task verification

Premature Termination

Stopped before the task was actually done. Direct MAST 'premature termination'.

planning coordination

Cascading Decision Error

An early wrong decision cascaded. Spans reasoning + orchestration in both.

planning coordination

Proxy Goal Convergence

Agent optimized a proxy instead of the true goal. MAST 'task derailment'.

task verification

Wrong Output Format

Output didn't match the required format/spec. MAST 'incorrect verification' adjacent.

planning coordination

Coordination Failure

Multi-agent coordination broke down. MAST (multi-agent-centric) formalizes this best.

planning coordination

Information Loss Handoff

Info dropped between agents/steps at a handoff. Direct MAST 'context loss on handoff'.

reasoning

Prompt Drift

The effective prompt/instruction drifts across a run and causes the failure. 18th class (#37); present in prior art (age…

other

Other

Catch-all when no specific class fits.