Structured output and tools

Ask for JSON that matches a schema, validate it, retry with the error, then fall back. Design tools like a small public API with strict inputs.

By Erik Bergstedt, Agent Wranglers. Updated 20 October 2026.

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Ask for output that matches a schema
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When code reads a model's answer, request output that matches a JSON Schema through the provider's structured output mode. Define that schema once in code.
Retry a bad answer and then fall back
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When an answer fails validation, retry at most twice with the validation error added, then use a fallback. Never pass an invalid answer on.
Give the model a way to say it does not know
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Give every schema field the model may not be able to fill an explicit "unknown" value or null. Never force it to invent a plausible answer.
Design tools like a small public API
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Give each tool one clear job, a verb-noun name, a description of when to use it and a strict input schema. Validate every argument in code before the tool runs.
Make tools that change things safe to repeat
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Give every tool that creates or changes data an idempotency key, so a repeated call has no extra effect.