Techniques & Methods
Structured Output in plain English.
Also known as: JSON mode,schema-constrained output
The one-sentence version
Forcing a model to reply in an exact machine-readable format, such as JSON matching a schema, so software can use the answer directly.
Structured output is when a model is constrained to respond in a precise, machine-readable shape — most often JSON that matches a schema you provide — instead of free prose. Without it, developers had to beg the model to "only return JSON" and then write fragile code to fix the cases where it added a friendly sentence or a stray comma. Modern APIs from OpenAI, Anthropic, and Google enforce the schema at generation time, so the output always parses and always has the fields you asked for. This is the quiet plumbing that makes AI features reliable: extracting invoice fields, classifying support tickets, filling database records, or having one agent hand structured results to another. It is also why some vendors now steer developers away from forcing tool calls and toward structured outputs for the same job.