# Evaluate predicate, choice and score questions
Purpose: API operation reference for `POST /v1/decisions`.
Last updated: 2026-09-15

## Endpoint

```txt
POST /v1/decisions
```

## Description

Send evidence in `input` and an ordered list of predicate, choice, and score questions. Each answer comes back in question order with its probabilities. Attach audio as `input_audio`, or an image as an `input_image` part of an `input` message.

Forward named questions and preserve the native answer, probabilities and usage.

## Request body

Content type: `application/json`

| Field | Required | Type | Description |
| --- | --- | --- | --- |
| `model` | Yes | `string` | model identifier or alias |
| `input` | Yes | `string \| array<DecisionInputMessage>` | shared text or user evidence messages |
| `questions` | Yes | `array<DecisionPredicateQuestion \| DecisionChoiceQuestion \| DecisionScoreQuestion>` | questions in answer order |
| `safety_identifier` | No | `string \| null` | opaque end-user safety identifier |
| `input_audio` | No | `DecisionInputAudio \| null` | Sprag extension: inline native audio evidence |

## Success response

Status: `200`
Content type: `application/json`

## Error responses

| Status | Description |
| --- | --- |
| `400` | The request was malformed, or a field value was invalid. |
| `401` | Missing, invalid, or expired credentials. |
| `402` | The account is out of credit. |
| `403` | Authenticated, but not a member of the requested organization. |
| `404` | The requested model does not exist or is not available. |
| `413` | The request body, or an inline media part, exceeds the accepted size. |
| `429` | Rate limit exceeded. |
| `500` | The model backend, or the gateway itself, failed while serving the request. |
| `502` | The model backend answered with something the gateway could not serve. |
| `503` | Temporarily unavailable; retry after `Retry-After` when present. |
| `504` | The model backend did not respond in time. |

## Related links

- [Markdown reference](https://sprag.ai/docs/api/decisions.md)
- [OpenAPI spec](https://sprag.ai/openapi.json)
- [Authentication](https://sprag.ai/docs/authentication.md)
- [Errors](https://sprag.ai/docs/errors.md)