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

# Order book update

> Subscribe to incremental orderbook updates for a symbol via WebSocket, pushed every 200ms.

`{symbol}@orderbookupdate` updated orderbook push every 200ms

```json theme={null}
{
  "id": "clientID2",
  "topic": "PERP_NEAR_USDC@orderbookupdate",
  "event": "subscribe"
}
```

**Parameters**

| Name  | Type   | Required | Description                |
| ----- | ------ | -------- | -------------------------- |
| id    | string | Y        | id generate by client      |
| event | string | Y        | `subscribe`/`unsubscribe`  |
| topic | string | Y        | `{symbol}@orderbookupdate` |

<RequestExample>
  ```json Response theme={null}
  {
    "id": "clientID2",
    "event": "subscribe",
    "success": true,
    "ts": 1609924478533
  }
  ```
</RequestExample>

<ResponseExample>
  ```json Subscribed Message theme={null}
  {
      "topic":"PERP_NEAR_USDC@orderbookupdate",
      "ts":1618826337580,
      "data":{
          "symbol":"PERP_NEAR_USDC",
          "prevTs":1618826337380,
          "asks":[
              [
                  15.15,
                  3.92864
              ],
              [
                  15.8,
                  0
              ],
              ...
          ],
          "bids":[
              [
                  14.2,
                  1.03895025
              ],
              [
                  13.6,
                  1.0807
              ],
              ...
          ]
      }
  }
  ```
</ResponseExample>