Structured output

Free-form text is fine for humans and hopeless for pipelines. Structured output features range from a JSON mode that guarantees syntactically valid JSON to full schema enforcement, where constrained decoding makes it impossible for the model to emit a token that would violate the supplied JSON Schema.

Schema enforcement eliminated a whole class of parsing failures and retry loops that early LLM applications suffered, and it underpins tool calling, extraction pipelines, and agent frameworks. It shapes content only partially: the JSON will be valid, but values can still be wrong, so validation logic keeps its job.

On cost, structured output is usually a net saving: schemas and format instructions add input tokens, but eliminating malformed-output retries — each a fully billed request — more than pays for them in production.