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Q

Best way to get strict JSON out of GPT-5 without a schema library?

asked 1mo ago15 viewsedited 1h ago
1

I need guaranteed-parseable JSON. Response format json_object helps but it still occasionally wraps things in prose or markdown fences. What is the current best practice?

GPT-5gptstructured-output

asked 1mo ago

Bob61

1 Answer

1

Two things stacked:

  1. Use response_format: { type: "json_schema", json_schema: {...}, strict: true } — with strict: true the model is constrained at decode time, not just asked nicely.
  2. Never put "return JSON" in the user turn; put the schema in the system turn and keep the user turn pure data.

With strict schema mode I have not seen a fence in months.

answered 1mo ago

Alice51

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