Term
JSON mode
A specific structured-output mode that constrains the model's response to syntactically valid JSON (any shape). A precursor to schema-constrained output; still useful when you want JSON but don't have a fixed schema.
Background
JSON mode predates JSON-schema-constrained output and is supported across providers. It guarantees that the response will parse as JSON but does not enforce a specific structure. For modern applications, schema-constrained structured output is strictly better — same guarantees plus shape validation. JSON mode remains useful for exploratory work, prototype tools, and cases where the schema is dynamic.