> For the complete documentation index, see [llms.txt](https://docs.getblock.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.getblock.io/api-reference/nervos-ckb/subscribe-nervos.md).

# subscribe - Nervos

Subscribes to a topic over WebSocket. Available topics: `new_tip_header` (new tip headers), `new_tip_block` (new tip blocks with transactions), `new_transaction` (new transactions entering the pool), `proposed_transaction` (transactions moved to proposed state), `rejected_transaction` (transactions rejected from the pool). Returns a subscription ID; events arrive as separate WebSocket messages.

{% hint style="info" %}
**WebSocket-only method.** This method is part of the Subscription module and is only available over the WebSocket transport at `wss://shared.eu-central-1.getblock.io/<ACCESS-TOKEN>/`. It will not work via HTTP POST.
{% endhint %}

## Parameters

| Parameter | Type   | Required | Description                                                                                                 |
| --------- | ------ | -------- | ----------------------------------------------------------------------------------------------------------- |
| topic     | string | Yes      | One of `new_tip_header`, `new_tip_block`, `new_transaction`, `proposed_transaction`, `rejected_transaction` |

## Request Example

{% tabs %}
{% tab title="cURL" %}

```bash
# WebSocket-only method. Use wscat (or similar) to connect first:
wscat -c 'wss://shared.eu-central-1.getblock.io/<ACCESS-TOKEN>/'

# Then send:
{"jsonrpc": "2.0", "method": "subscribe", "params": ["new_tip_header"], "id": "getblock.io"}
```

{% endtab %}

{% tab title="JavaScript (Axios)" %}

```javascript
import WebSocket from 'ws';

const ws = new WebSocket('wss://shared.eu-central-1.getblock.io/<ACCESS-TOKEN>/');

ws.on('open', () => {
    ws.send(JSON.stringify({
    "jsonrpc": "2.0",
    "method": "subscribe",
    "params": [
        "new_tip_header"
    ],
    "id": "getblock.io"
}));
});

ws.on('message', (data) => {
    console.log(JSON.parse(data.toString()));
});
```

{% endtab %}

{% tab title="Python (Requests)" %}

```python
import asyncio
import json
import websockets

async def main():
    async with websockets.connect('wss://shared.eu-central-1.getblock.io/<ACCESS-TOKEN>/') as ws:
        await ws.send(json.dumps({
    "jsonrpc": "2.0",
    "method": "subscribe",
    "params": [
        "new_tip_header"
    ],
    "id": "getblock.io"
}))
        async for message in ws:
            print(json.loads(message))

asyncio.run(main())
```

{% endtab %}

{% tab title="Rust (Reqwest)" %}

```rust
use tokio_tungstenite::connect_async;
use tokio_tungstenite::tungstenite::Message;
use serde_json::json;
use futures_util::{SinkExt, StreamExt};

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let (mut ws_stream, _) = connect_async("wss://shared.eu-central-1.getblock.io/<ACCESS-TOKEN>/").await?;

    let payload = json!({
        "jsonrpc": "2.0",
        "method": "subscribe",
        "params": [
                "new_tip_header"
        ],
        "id": "getblock.io"
});
    ws_stream.send(Message::Text(payload.to_string())).await?;

    while let Some(msg) = ws_stream.next().await {
        println!("{:?}", msg?);
    }
    Ok(())
}
```

{% endtab %}
{% endtabs %}

## Response Example

{% code overflow="wrap" %}

```json
{
    "jsonrpc": "2.0",
    "id": "getblock.io",
    "result": "0xf1"
}
```

{% endcode %}

## Response Parameters

| Field  | Type   | Description                                                                      |
| ------ | ------ | -------------------------------------------------------------------------------- |
| result | string | Subscription ID — used to match incoming notifications and to call `unsubscribe` |

## Use Cases

* Real-time block notifications for indexers
* Live wallet activity (subscribe to `new_transaction` filtered to your address)
* Mempool monitoring dashboards
* Detecting rejected transactions for RBF logic

## Error Handling

| Status Code | Error Message     | Cause                                                                |
| ----------- | ----------------- | -------------------------------------------------------------------- |
| 403         | Forbidden         | Missing or invalid `<ACCESS-TOKEN>`                                  |
| -32602      | Invalid params    | Request parameters are missing or malformed                          |
| -32601      | Method not found  | Method does not exist or is not enabled on this node                 |
| -32603      | Internal error    | Server-side error while processing the request                       |
| 429         | Too Many Requests | Rate limit exceeded for your plan                                    |
| -32600      | Invalid Request   | `subscribe` was called over HTTP; use a WebSocket connection instead |
| -32602      | Invalid topic     | Topic string is not one of the supported topics                      |

## SDK Integration

{% tabs %}
{% tab title="@ckb-lumos/lumos / ws" %}

```javascript
// Lumos doesn't expose CKB subscription methods directly. Use a raw
// WebSocket as shown in the Request Example above, or use the @ckb-ccc/core
// subscription helpers if available.
import WebSocket from 'ws';

const ws = new WebSocket('wss://shared.eu-central-1.getblock.io/<ACCESS-TOKEN>/');
ws.on('open', () => {
    ws.send(JSON.stringify({
        jsonrpc: '2.0',
        id: 'sub-1',
        method: 'subscribe',
        params: ["new_tip_header"]
    }));
});
ws.on('message', (data) => console.log(JSON.parse(data.toString())));
```

{% endtab %}

{% tab title="websockets (Python)" %}

```python
# CKB SDK Python doesn't expose subscriptions directly — use websockets.
import asyncio, json, websockets

async def main():
    async with websockets.connect('wss://shared.eu-central-1.getblock.io/<ACCESS-TOKEN>/') as ws:
        await ws.send(json.dumps({
            'jsonrpc': '2.0', 'id': 'sub-1',
            'method': 'subscribe', 'params': ["new_tip_header"]
        }))
        async for msg in ws:
            print(json.loads(msg))

asyncio.run(main())
```

{% endtab %}
{% endtabs %}