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

# POST Send runner message

> Append instructions to a running runner run

```bash theme={null}
POST /runner/runs/{run_id}/messages
```

**Request body**

| Field     | Type     | Required | Description                             |
| --------- | -------- | -------- | --------------------------------------- |
| `message` | `string` | Yes      | Message to append, 1-10,000 characters. |