Enum ResponseFormat 

#[non_exhaustive]
pub enum ResponseFormat {
    Text,
    JsonObject,
    JsonSchema {
        name: String,
        schema: Value,
        strict: bool,
    },
}

Constrains the output format of a language model response.

Providers that don’t support a given format return LanguageModelError::Provider.

Provider support

Format	OpenAI	Anthropic	Ollama
Text	All models	All models	All models
JsonObject	Most models	Not supported	Supported
JsonSchema	Newer models	Beta (sonnet-4-5+, opus-4-1+)	Supported

Variants (Non-exhaustive)

Non-exhaustive enums could have additional variants added in future. Therefore, when matching against variants of non-exhaustive enums, an extra wildcard arm must be added to account for any future variants.

Text

No constraint — free-form text (default).

JsonObject

Must produce valid JSON (no schema constraint).

OpenAI requires that you also instruct the model to produce JSON in your system or user messages — setting this alone is not sufficient.

JsonSchema

Must produce JSON conforming to the given schema.

Fields

name: String

A name for this schema (used by OpenAI, max 64 chars, [a-zA-Z0-9_-]).

schema: Value

The JSON Schema definition.

strict: bool

Whether to enforce strict schema adherence.

Trait Implementations

impl Clone for ResponseFormat

fn clone(&self) -> ResponseFormat

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for ResponseFormat

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for ResponseFormat

fn default() -> ResponseFormat

Returns the “default value” for a type.