Structured Output (JSON Mode)

Structured output (also called JSON mode or structured generation) forces an AI model to respond in a specific format — usually JSON — rather than free-form text. This makes AI output reliably machine-readable, which is essential for building AI into software systems.

Why it matters

When you chat with AI, free-form text is fine. When software needs to process AI output — inserting it into a database, triggering an automation, populating a template — it needs predictable structure. "The product costs £49.99" is useful to a human but useless to code that needs `{"price": 49.99, "currency": "GBP"}`.

How it works

You define a schema (the shape of the output you want) and the model constrains its generation to match that schema. Instead of predicting any next token, the model only predicts tokens that produce valid output according to your schema.

A practical example

Without structured output: "Extract the name, company, and role from this email signature." → AI might respond in any format, inconsistently.

With structured output: "Extract the following as JSON: {name: string, company: string, role: string}" → AI always returns valid JSON matching the schema, every time.

When to use it

Any time AI output feeds into another system: API responses, database entries, automation triggers, form population, data extraction, content management systems. If a human is the only consumer, free text is fine. If code needs to process the output, use structured output.