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EngineeringFebruary 12, 2026· 5 min read
Errors are the interface agents actually read
If your API errors are vague, your agent will be too. A case for error messages written for machines.
MT
Marco T.
Engineering
Humans read docs; agents read errors. When a call fails, the error string is the only feedback the model gets, so it had better say what to do next.
What a good error says
- What failed, in plain language
- Why, with the specific value that was wrong
- The one next action most likely to fix it
We rewrote ours
Every Ferr error now names the field, the reason, and a suggested fix. Agents recover from them without a human in the loop far more often.
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