Structured Outputs (OpenAI) / Constrained decoding — how do they differ from JSON mode?

hard

Answer

$JSON mode: guarantees valid JSON syntax.$
$Structured Outputs / Constrained decoding: guarantees the JSON matches a specific schema (types, required fields, enums, nested structures).$
$Implementation: build a grammar / automaton from the JSON schema and mask logits to only allow tokens that keep the output on a valid grammar path.$
$OpenAI's Structured Outputs, XGrammar, Outlines.$
$Standard for tool calling and complex extraction where schema violations would break downstream code.$

Check yourself — multiple choice

Same as JSON mode
Constrained-decoding tracks a JSON-schema automaton → guarantees schema (not just syntax) → foundation for reliable tool calling
Only post-processing
Impossible

Structured Outputs / constrained decoding: schema-level guarantees, not just JSON syntax.

#generation#production

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