Inkbox

> # Documentation index
> Fetch the complete documentation index at: https://inkbox.ai/sitemap.xml
> Use this file to discover all available pages before exploring further.

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# Messaging capability
description: Check whether a phone number is currently reachable over iMessage, SMS, or RCS

---


# Messaging capability

Check which messaging service is currently available for an E.164 phone number. This is a read-only lookup and does not require an agent identity or an existing conversation.

## Check messaging capability `GET`


### Query parameters

| Parameter | Type | Required | Description |
| :--- | :--- | :--- | :--- |
| `number` | string | Yes | Recipient phone number in E.164 format |

URL-encode the leading `+` as `%2B` when you place the number in the query string:

```bash
curl "https://inkbox.ai/api/v1/imessage/check-messaging-capability?number=%2B14155550100" \\
    -H "X-API-Key: YOUR_API_KEY"
```

Use an admin API key or claimed agent key. Unclaimed (mid-signup) agent keys are rejected.

### Response (200)

The response body is a JSON string—not an object—and is always one of `iMessage`, `SMS`, or `RCS`:

```json
"iMessage"
```

Check capability close to the time you intend to message the recipient because service availability can change.

### Error responses

| Status | Description |
| :--- | :--- |
| 401 | Authentication is missing or invalid |
| 403 | The credential is valid but is not permitted to perform capability lookups |
| 422 | `number` is missing or is not a valid phone number |
| 502 | Capability information is temporarily unavailable |