Practice · Established · Intermediate

Structured Output

Also known as: JSON mode

Constraining a model to emit data that conforms to a specified schema so downstream code can rely on it.

What Structured Output is

Free text is unusable in a pipeline. Structured output guarantees valid JSON matching a declared shape, with the model filling values rather than inventing formats.

How it works

Providers implement this with constrained decoding against a JSON schema or grammar. Applications still validate on receipt and handle refusals and truncation explicitly.

Why it matters

It is what makes generative models safe to place inside deterministic systems, and it removes an entire class of parsing bugs.

Common uses

→Document data extraction
→Classification with fixed labels
→Form population
→Agent tool arguments

Strengths

✓Guaranteed parseable
✓Fewer retries

Watch for

✓Rigid schemas can distort borderline cases
✓Long schemas consume context

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