> ## Documentation Index
> Fetch the complete documentation index at: https://docs.mirobody.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# Structured Output

> text.format — constrain the model to JSON (json_object) or a JSON Schema (json_schema) in backbone mode.

Use `text.format` on [`POST /v1/responses`](/en/api-reference/responses) to force the model's output into JSON. It follows the [OpenAI Responses `text.format` spec](https://platform.openai.com/docs/api-reference/responses/create#responses-create-text) and is available **only in [backbone mode](/en/api-reference/backbone-mode) (`mode:"model"`)**.

<Warning>
  `text.format` requires `mode:"model"`. On the default agent mode it returns `400 unsupported_parameter` (`param: "text"`) — free-text that explodes downstream is more expensive than an interface error. The Answers API (`/v1/chat/completions`) likewise rejects `response_format` with `400`.
</Warning>

## `json_object`

Constrains the output to a syntactically valid JSON object (no schema):

```jsonc theme={null}
{
  "model": "mirobody-flash",
  "mode": "model",
  "input": "Reply with a JSON object having keys a and b.",
  "text": { "format": { "type": "json_object" } }
}
```

The message text is a JSON string you parse yourself:

```jsonc theme={null}
{ "output_text": "{\"a\":1,\"b\":2}", "status": "completed", ... }
```

## `json_schema`

Constrains the output to a schema you supply. Set `strict: true` for exact schema adherence:

<CodeGroup>
  ```bash curl theme={null}
  curl https://mirobody-api.thetahealth.ai/v1/responses \
    -H "Authorization: Bearer $MIROBODY_API_KEY" \
    -H "Content-Type: application/json" \
    -d '{
          "model": "mirobody-flash",
          "mode": "model",
          "input": "Give me a manifest for apples with count 3.",
          "text": {
            "format": {
              "type": "json_schema",
              "name": "manifest",
              "strict": true,
              "schema": {
                "type": "object",
                "properties": {
                  "item":  { "type": "string" },
                  "count": { "type": "integer" }
                },
                "required": ["item", "count"],
                "additionalProperties": false
              }
            }
          }
        }'
  ```

  ```python Python (OpenAI SDK) theme={null}
  from openai import OpenAI

  client = OpenAI(api_key="mb_live_...", base_url="https://mirobody-api.thetahealth.ai/v1")

  resp = client.responses.create(
      model="mirobody-flash",
      extra_body={"mode": "model"},
      input="Give me a manifest for apples with count 3.",
      text={
          "format": {
              "type": "json_schema",
              "name": "manifest",
              "strict": True,
              "schema": {
                  "type": "object",
                  "properties": {"item": {"type": "string"}, "count": {"type": "integer"}},
                  "required": ["item", "count"],
                  "additionalProperties": False,
              },
          }
      },
  )
  print(resp.output_text)   # {"item":"apples","count":3}
  ```
</CodeGroup>

## Provider fallback

`text.format` passes through to the underlying model. When the backing provider has **no** native `json_schema` support, Mirobody automatically retries **once** as `json_object` with the schema injected into the system prompt. The retry is transparent — you still get schema-shaped JSON back — so treat structured output as reliable without knowing which provider backs a tier.

## See also

* [Backbone mode](/en/api-reference/backbone-mode) — `mode:"model"`, the prerequisite for `text.format`.
* [Function calling](/en/api-reference/function-calling) — for tool-argument shaping, pair `text.format` with `tool_choice:"required"`.