Model output does not match JSON schema
Ensure `strict: true` is set for function calls or use `response_format` with `json_schema` for direct outputs.
Use the new Structured Outputs feature by setting `strict: true` in function definitions or by using `response_format: {"type": "json_schema", "schema": YOUR_SCHEMA}` for direct responses. Model output does not reliably conform to the expected JSON schema.
Previous JSON mode did not guarantee schema adherence; models might generate valid JSON but not the *correct* structure.
If model outputs fail to match a required JSON schema, implement OpenAI's Structured Outputs feature by enabling `strict: true` for function calls or using the `json_schema` type in `response_format`.
Structured Outputs employ constrained decoding to force model outputs to strictly adhere to the provided JSON schema, achieving 100% reliability.
- Introducing Structured Outputs in the API ↗OpenAI · OpenAI News · Aug 6, 2024 · paraphrased
First seen on Subvolts Aug 6, 2024. Updated Sep 11, 2026. Spotted a problem? Tell us.
- Introducing Structured Outputs in the APIOpenAI · OpenAI News · Aug 6, 2024
The Playbook: reusable how-tos, prompts, configs and tips pulled out of the news.
- HeuristicConstrained decoding ensures reliable structured outputsModels are constrained to only valid tokens according to the schema, not all possible tokens, for guaranteed output format. · 10 min
- ToolOpenAI API Structured OutputsEnsures model outputs reliably adhere to developer-supplied JSON Schemas for function calls and direct responses. · 10 min
- Code snippetEnable structured outputs for function calling with strict modeSet strict: true in your function definition to ensure model outputs match the tool definition. · 5 min
- Code snippetUse response_format json_schema for structured model responsesSet `response_format: {"type": "json_schema", "schema": YOUR_SCHEMA}` to get structured outputs without function calling. · 5 min
- Code snippetDescribe functions to GPT-4 and GPT-3.5-turbo for function callingUse JSON Schema to describe functions to the model and optionally ask it to call a specific function. · 5 min
- Model pickUse gpt-4o-2024-08-06 for 100% structured output reliabilityThe latest GPT-4o model achieves perfect scores on structured output evaluations with the new feature. · 5 min
Questions people ask
- Which AI tools does this work with?
- The sources used it with ChatGPT.
- Where did this come from?
- OpenAI (OpenAI News). Subvolts collected, normalized and credited it; the link above opens the original.