5 ways your n8n AI agent breaks in production (and the quick test for each)

Description and use

Five common production failures in n8n LLM workflows and quick tests to detect them.

n8n AI workflows pass in the editor but fail under real traffic due to untested failure paths.

After applying targeted tests and fixes, the n8n AI workflows operate reliably in production, handling edge cases and failures gracefully.

1. Test LLM output by feeding 20 messy inputs and enforce JSON schema in the prompt.
2. Mock API failures (429/500) to verify error handling and enable "Never Error" off.
3. POST the same payload three times to detect duplicate runs and add an idempotency key.
4. Run with minimal input (no name, no email) to test empty/edge inputs and add validation IF nodes.
5. Set up an n8n Error Workflow to ping on any failure and enable retry with backoff on API nodes.

Every one of these failures bit me while building n8n workflows with LLM nodes. They all pass in the editor and break under real traffic.

The LLM returns prose, not JSON

Silent API failure

Duplicate runs

Empty and edge inputs

It works - until the key expires or the limit hits