Structured JSON

JSON object mode

Choose a model whose json_mode capability is true. Tell the model what object to return and set response_format.

{
  "model": "worker",
  "messages": [
    {"role": "system", "content": "Return JSON with keys severity and summary."},
    {"role": "user", "content": "The health check has failed for six minutes."}
  ],
  "response_format": {"type": "json_object"}
}

JSON schema mode

Clients that support JSON schema can send response_format.type as json_schema with a schema definition. Keep schemas small and explicit. Use required fields and disable additional properties when unexpected keys would be unsafe.

Always parse and validate the returned content in your application. A valid JSON document can still contain an invalid business value. Do not use generated JSON directly in SQL, shell commands, access-control decisions, or financial actions.