A simple tool-call fingerprint can stop many LLM agent loops, but not all of them
Future_AGI · reddit · 2026-07-28
What a tool-call fingerprint can catch in LLM agents
The post argues that agent loops are usually caused by missing memory of prior actions, unreadable tool outputs, or no objective stop check — not by the step cap itself. Raising the limit only makes the same failure run longer and cost more.
Core idea
- Hash each tool name + arguments into a per-run fingerprint before dispatch.
- Keep a seen set for the run and block any exact repeat call.
- Use sortkeys=True when serializing arguments, or the same call with reordered fields will look different.
What it misses
- Volatile fields like timestamps or request IDs can create fake uniqueness and bypass the guard.
- It only inspects the call side; two different calls that produce the same dead-end result will still slip through.
The author asks whether call fingerprinting catches most agent loops in practice, or whether output fingerprinting is also needed.
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