Failure Index / Data & schema · critical · LangChain · OpenAI Agents SDK · CrewAI

Agent tool call fails with 404: resource not found (bad ID from a previous step)

The agent asked for something that doesn't exist. In agent systems this is rarely a bad URL — it's usually a bad ID that the MODEL extracted incorrectly from a previous step's output.

The error

agent 404 not found tool call
langchain tool resource not found
agent passing wrong id 404

Root cause

A prior step returned data, the model parsed an identifier out of it, and got it subtly wrong — truncated it, grabbed the wrong field, or reformatted it (stripping leading zeros, changing case). The 404 fires one step later, hiding the real cause.

The fix

Look at the previous step's output and compare the ID the agent extracted with the ID that actually exists. Fix the extraction: pass structured fields between steps instead of letting the model re-read free text.

Preventing it next time

Pass IDs between steps as structured data (tool returns JSON, next tool receives the field directly) — never round-trip identifiers through model-generated prose.

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