Structured Output

Asking a model for JSON in a system prompt works most of the time, which is the problem. generateStructured validates the result against a schema and can repair it.

val result = RunAnywhere.llm.generateStructured(
    prompt = "Extract the name and age: Dana is 34.",
    schema = schema,
    mode = StructuredOutputMode.VALIDATION_ONLY,
    options = LlmOptions(temperature = 0.1f)
)

Enforcement modes

Mode	Behaviour
`VALIDATION_ONLY`	Generate freely, then validate. The default.
`REPAIR`	Validate, then retry once with a repair instruction.
`CONSTRAINED`	Throws `unsupportedCapability` today.

Constrained mode throws on every SDK. It needs engine-level constrained decoding, which is not wired in yet. Use validation-only or repair.

Validation-only is the default and is right when a retry is cheap. Repair costs a second generation when the first is invalid, which is worth it when the call is user-facing and a failure means showing an error.

The schema

val schema = JsonSchema(/* your JSON schema */)

Keep schemas small. A small model handles four flat fields reliably and a deeply nested structure badly. When you need something complex, ask for the pieces separately rather than one large object. Naming fields the way a person would helps: totalPrice gets better results than tp.

Reading the result

// result carries the parsed value and the raw text

When to reach for this

Task	Approach
Extracting fields from text	Structured output
Classifying into fixed labels	Structured output, or a one-word prompt
Anything you will `JSON.parse`	Structured output
Prose for a human to read	Plain generation

If you are about to write a regex over a model’s reply, you want this instead.

Temperature

Lower it. Structured extraction is not a creative task, and 0.1 to 0.3 produces far more consistent field values than the default.

Getting Started

Swift SDK

Kotlin SDK

React Native SDK

Flutter SDK

Web SDK

Electron SDK

Vibe Coding

Enforcement modes

The schema

Reading the result

When to reach for this

Temperature

​Enforcement modes

​The schema

​Reading the result

​When to reach for this

​Temperature

Enforcement modes

The schema

Reading the result

When to reach for this

Temperature