# Flag routes: evaluate

URL: /code/api/flag/verbs · Id: `page:code/api/flag/verbs`

> The Flag Verbs evaluate as api.sb routes, with inputs, result, refusals and an example.

Reference for [Flag](/business/nouns/flag), one group of [Flag routes](/code/api/flag).

### Flag.evaluate
Evaluate returns the Variant a Flag assigns one unit, the same one every time, and records the Exposure with every option and its propensity. [Verb page](/business/nouns/flag/evaluate?interface=api).

```text
POST /{namespace}/flags/{flag}/evaluate
```

Path: `flag`. Body, as JSON: the other inputs. Emits [`Flag.evaluated`](/business/events/Flag.evaluated).

**Inputs**

| Input | Type | Required | Description |
| --- | --- | --- | --- |
| `flag` | [Flag](/business/nouns/flag) | Yes | The Flag to evaluate, by key. |
| `unit` | `string` | Yes | The id of the Visitor, Customer, Contact, Conversation or request being assigned. |
| `default` | `string` | No | The Variant key returned when the Flag is off or the value may not be varied. |

**Returns**

| Output | Type | Required | Description |
| --- | --- | --- | --- |
| `variant` | [Variant](/business/nouns/variant) | Yes | The Variant assigned to the unit. |
| `exposure` | [Exposure](/business/nouns/exposure) | No | The Exposure recorded; none in Mode try. |

**Refuses when**

| Check | Error | Fix | Then call |
| --- | --- | --- | --- |
| The key is valid, but its scopes do not allow this operation. | [`forbidden`](/code/api/errors/forbidden) | Use a key whose scopes cover the operation, or ask an owner of the namespace to grant them. | None. |

**Example**

```bash
curl -X POST https://api.sb/leaseline.app/flags/flag_1YJLhjTlfx/evaluate \
  -H "Authorization: Bearer $STARTUP_BUILDER_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"unit":"Example unit"}'
```

```json
{
  "api": "https://api.sb/leaseline.app",
  "variant": {
    "$id": "https://api.sb/leaseline.app/variants/variant_nvdfmt7dTw",
    "$type": "Variant",
    "key": "Example key",
    "value": {}
  },
  "exposure": {
    "$id": "https://api.sb/leaseline.app/exposures/exposure_Ua2Xw4KsJB",
    "$type": "Exposure",
    "unit": "Example unit",
    "options": {},
    "propensity": 1,
    "at": "2026-10-22T12:00:00Z"
  },
  "action": {
    "$id": "https://api.sb/leaseline.app/actions/act_br07HsG8MG",
    "operation": "Flag.evaluate",
    "status": "done"
  },
  "links": {
    "self": "https://api.sb/leaseline.app/actions/act_br07HsG8MG"
  }
}
```