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

# Smart Order Routing Heartbeat

> Logical-level liveness signal for Smart Order Routing platform.

The Heartbeat channel provides a logical-level liveness signal for authorized Smart Order Routing customers. Subscribe to receive periodic heartbeat messages to monitor the health of your WebSocket connection and the server's responsiveness.

## Subscribe to Heartbeat

### Request

```json theme={null}
{
  "type": "subscribe",
  "channels": [
    {
      "type": "heartbeat"
    }
  ]
}
```

> The heartbeat channel does not require parameters.

### Response

```json theme={null}
{
  "type": "subscribe",
  "channels": [
    {
      "type": "heartbeat",
      "success": true
    }
  ]
}
```

### Error Response

```json theme={null}
{
  "type": "subscribe",
  "channels": [
    {
      "type": "heartbeat",
      "success": false,
      "error": "UNKNOWN_CHANNEL"
    }
  ]
}
```

## Heartbeat Message Format

The server sends periodic heartbeat messages after you subscribe:

```json theme={null}
{
  "channel": "heartbeat",
  "payload": {
    "timestamp": "2024-01-15T10:30:00.123456789Z"
  }
}
```

### Message Fields

| Field       | Type   | Description                            |
| ----------- | ------ | -------------------------------------- |
| `timestamp` | string | Server timestamp in RFC3339Nano format |

## Unsubscribe

To stop receiving heartbeat messages:

```json theme={null}
{
  "type": "unsubscribe",
  "channels": [
    {
      "type": "heartbeat"
    }
  ]
}
```

## List Active Subscriptions

Get all active subscriptions including heartbeat:

```json theme={null}
{
  "type": "subscription_list"
}
```

### Response

```json theme={null}
{
  "type": "subscription_list",
  "channels": [
    {
      "type": "heartbeat"
    },
    {
      "type": "market_data",
      "params": {
        "market": "BTCUSD"
      }
    }
  ]
}
```

## Heartbeat vs WebSocket Ping/Pong

The heartbeat channel operates at the application layer, while WebSocket ping/pong operates at the protocol layer:

* **WebSocket Ping/Pong**: Automatic transport-layer keepalive handled by the WebSocket protocol
* **Heartbeat Channel**: Application-layer liveness signal providing server timestamp and logical health status

Use heartbeat messages to verify that the server is not only connected but also actively processing and responding to your connection at the application level.

> Questions? Contact [Support](https://support.paxos.com).