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AI Agent Failure Index

Every common way an AI agent breaks — what the error actually means, the root cause, and the fix that works. Sourced from real diagnosed failures across LangChain, the OpenAI Agents SDK, and CrewAI. Bookmark it for the next 2am debugging session.

Auth & permissions

Agent tool call fails with HTTP 401 UnauthorizedToolException: 401 Unauthorized · LangChain / OpenAI Agents SDK / CrewAIAgent tool call fails with HTTP 403 ForbiddenToolError: 403 forbidden agent · LangChain / OpenAI Agents SDK / CrewAIStripe tool fails: authentication error / invalid API keystripe invalid api key agent · LangChain / OpenAI Agents SDKGmail / Google API tool fails: invalid credentials or token expiredgmail api invalid_grant agent · LangChain / OpenAI Agents SDK / CrewAI

Rate limits & availability

Agent hits HTTP 429: rate limit exceeded (often from its own retry loop)agent 429 too many requests loop · LangChain / OpenAI Agents SDK / CrewAIGmail API rate limit: ~25 requests/minute per usergmail api rate limit exceeded agent · LangChain / OpenAI Agents SDKAgent tool fails with HTTP 500 / 502 / 503 from the upstream servicetool 503 service unavailable agent · LangChain / OpenAI Agents SDK / CrewAIAgent tool call times out (TimeoutError / ReadTimeout)TimeoutError langchain tool · LangChain / OpenAI Agents SDK / CrewAIAgent tool fails: connection refused / resetConnectionRefusedError agent tool · LangChain / OpenAI Agents SDK / CrewAI

Data & schema

Agent tool call fails with 404: resource not found (bad ID from a previous step)agent 404 not found tool call · LangChain / OpenAI Agents SDK / CrewAIAgent step fails with KeyError: expected field missing from previous outputKeyError agent tool langchain · LangChain / OpenAI Agents SDK / CrewAIAgent fails with TypeError / 'NoneType' object has no attribute'NoneType' object has no attribute agent · LangChain / OpenAI Agents SDK / CrewAIOutputParserException: could not parse LLM outputOutputParserException Could not parse LLM output · LangChain

Agent behavior

Agent stopped due to iteration limit or time limitAgent stopped due to iteration limit or time limit · LangChain / OpenAI Agents SDK / CrewAIAgent calls a tool that doesn't exist (hallucinated tool name)agent tool not found error · LangChain / OpenAI Agents SDK / CrewAIContext length exceeded: agent run grows past the model's windowcontext_length_exceeded agent · LangChain / OpenAI Agents SDK / CrewAIMulti-agent handoff fails or loses context between agentsopenai agents sdk handoff not working · OpenAI Agents SDK / CrewAI / LangGraphGuardrail triggered: agent run blocked mid-taskopenai agents guardrail tripwire triggered · OpenAI Agents SDK / LangChain
Hitting one of these right now? Vorlo diagnoses them automatically — add 2 lines of code and every failed run comes back with the root cause and the fix, verified by developers who hit it before you. Start free or read the quickstart.