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

# Message Parts

> Build ordered text, media, and link parts for a Relay Message.

Every outbound Message contains 1 to 100 ordered `parts`.

## Part types

| Type    | Required content               | Use                                            |
| ------- | ------------------------------ | ---------------------------------------------- |
| `text`  | `value`                        | Plain text and one optional structured mention |
| `media` | `attachment_id` or HTTPS `url` | Image, video, audio, or document               |
| `link`  | `value`                        | One URL rendered as a rich preview             |

### Text

```json theme={null}
{
  "type": "text",
  "value": "Relay accepted the request."
}
```

Text must contain 1 to 10,000 UTF-16 code units. A mention adds `mention` and
`mention_range`; read [Mentions](/guides/messaging/mentions) before calculating
that range.

### Media

Reference one completed Relay Attachment:

```json theme={null}
{
  "type": "media",
  "attachment_id": "01993d50-d263-7d6b-87ce-90aba89b7815"
}
```

For public files up to 10 MB, use one HTTPS URL instead:

```json theme={null}
{
  "type": "media",
  "url": "https://cdn.example.com/photo.webp"
}
```

Use exactly one of `attachment_id` or `url`.

### Link

```json theme={null}
{
  "type": "link",
  "value": "https://relayapp.im"
}
```

**A link must be the only part in its Message.** Put a URL inside a text part
when it should remain ordinary text.

## Ordering and composition

`part_index` is the zero-based position in the array. Replies and reactions
use it to target one exact part.

Text and media may be mixed in order. Consecutive text parts are rejected;
combine adjacent text into one part. A link must remain the only part in its
Message.

## Response-only parts

Relay can return `type: "system"` for visible Chat history such as membership
or group metadata changes. A developer cannot send a system part.

Response parts can also contain current `reactions`. Media responses add the
Attachment ID, opaque download URL, filename, MIME type, size, and available
dimensions or duration.

## Related

* [Sending Messages](/guides/messaging/sending-messages)
* [Message Details](/guides/messaging/message-details)
* [Attachments](/guides/messaging/attachments)
* [Rich Link Previews](/guides/messaging/rich-link-previews)