What is the difference between JSON Mode and Structured Outputs?

JSON Mode guarantees syntactically valid JSON but does not enforce schema compliance, while Structured Outputs guarantee both valid JSON and schema conformance. JSON Mode (response_format: {type: "json_object"}) prevents conversational text and ensures parseable output but cannot guarantee specific fields exist or types match. Structured Outputs use JSON Schema to define exact structure, ensuring output matches your requirements precisely. JSON Mode may return valid JSON with wrong fields or structure. Structured Outputs validate against schema during generation, refusing to complete if schema cannot be satisfied. JSON Mode is faster and less restrictive. Structured Outputs provide stronger guarantees at potential latency cost. Use JSON Mode for flexible schemas where exact structure varies. Use Structured Outputs for critical applications requiring specific fields and types. Validate outputs with our JSON Editor at jsonconsole.com/json-editor regardless of mode. OpenAI, Anthropic, and others implement these differently. Structured Outputs are newer and not universally available. Choose based on reliability requirements versus flexibility needs.