> 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/bittensor-tao/chain_subscribenewheads-bittensor.md).

# chain\_subscribeNewHeads - Bittensor

Subscribes to new block headers as they are produced. Returns a subscription ID; matching headers arrive as separate WebSocket messages with method `chain_newHead`.

{% hint style="info" %}
**Substrate native JSON-RPC method.** Call against a GetBlock endpoint configured for the Substrate interface. For typed SDK access, use [Polkadot.js](https://polkadot.js.org/docs/api) (TypeScript) or [substrateinterface](https://github.com/polkascan/py-substrate-interface) (Python).
{% endhint %}

{% hint style="warning" %}
**WebSocket-only method.** This method requires the WebSocket transport at `wss://shared.eu-central-1.getblock.io/<ACCESS-TOKEN>/`. It will not work via HTTP POST.
{% endhint %}

## Parameters

* None

## 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": "chain_subscribeNewHeads", "params": [], "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": "chain_subscribeNewHeads",
    "params": [],
    "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": "chain_subscribeNewHeads",
    "params": [],
    "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": "chain_subscribeNewHeads",
        "params": [],
        "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": "9DZyB1n6BvF5dQ8wQRhgrxqCw"
}
```

{% endcode %}

## Response Parameters

| Field  | Type   | Description                                                               |
| ------ | ------ | ------------------------------------------------------------------------- |
| result | string | Subscription ID — match incoming `chain_newHead` notifications by this ID |

## Use Cases

* Real-time block notifications for indexers, explorers, and dashboards
* Triggering downstream processing on every new block
* Replacing inefficient polling with push-based delivery

## 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 on this interface — check whether you're calling a Substrate method on an EVM endpoint or vice versa |
| -32603      | Internal error    | Server-side error while processing the request                                                                             |
| 429         | Too Many Requests | Rate limit exceeded for your plan                                                                                          |

## SDK Integration

{% tabs %}
{% tab title="Polkadot.js (TypeScript)" %}

```javascript
import { ApiPromise, WsProvider } from '@polkadot/api';

const provider = new WsProvider('wss://shared.eu-central-1.getblock.io/<ACCESS-TOKEN>/');
const api = await ApiPromise.create({ provider });

// Typed wrapper: api.rpc.chain.subscribeNewHeads(...)
const result = await api.rpc.chain.subscribeNewHeads();
console.log(result.toHuman());

// Or use the raw RPC interface for any method:
// const raw = await api.rpc.send({ method: 'chain_subscribeNewHeads', params: [] });
```

{% endtab %}

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

```python
from substrateinterface import SubstrateInterface

substrate = SubstrateInterface(url="wss://shared.eu-central-1.getblock.io/<ACCESS-TOKEN>/")

# Generic RPC call:
result = substrate.rpc_request("chain_subscribeNewHeads", [])
print(result)
```

{% endtab %}
{% endtabs %}