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

# GET /api/sessions/check

> Checks whether an email or phone identifier is available for registration, rejecting reserved values and identifiers already linked to a DID.

Checks whether an identifier is available for registration. Routes to the `Vault` Durable Object for the supplied identifier.

## Query parameters

| Parameter    | Type     | Required | Description                                 |
| ------------ | -------- | -------- | ------------------------------------------- |
| `identifier` | `string` | Yes      | Identifier to check (also accepts `handle`) |
| `channel`    | `string` | No       | Channel (default: `"handle"`)               |

## Response (200)

```json theme={null}
{ "available": true, "reason": null }
```

```json theme={null}
{ "available": false, "reason": "taken" }
```

```json theme={null}
{ "available": false, "reason": "reserved", "message": "This identifier is reserved" }
```