> 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/system_accountnextindex-bittensor.md).

# system\_accountNextIndex - Bittensor

Returns the next available transaction index (nonce) for a given account address. Required before constructing and signing a new extrinsic — the nonce must be sequential per account.

{% 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 %}

## Parameters

| Parameter | Type   | Required | Description                  |
| --------- | ------ | -------- | ---------------------------- |
| address   | string | Yes      | SS58-encoded account address |

## Request Example

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

```bash
curl --location --request POST 'https://shared.eu-central-1.getblock.io/<ACCESS-TOKEN>/' \
--header 'Content-Type: application/json' \
--data-raw '{
    "jsonrpc": "2.0",
    "method": "system_accountNextIndex",
    "params": [
        "5GrwvaEF5zXb26Fz9rcQpDWS57CtERHpNehXCPcNoHGKutQY"
    ],
    "id": "getblock.io"
}'
```

{% endtab %}

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

```javascript
import axios from 'axios';

const data = JSON.stringify({
    "jsonrpc": "2.0",
    "method": "system_accountNextIndex",
    "params": [
        "5GrwvaEF5zXb26Fz9rcQpDWS57CtERHpNehXCPcNoHGKutQY"
    ],
    "id": "getblock.io"
});

const config = {
    method: 'post',
    url: 'https://shared.eu-central-1.getblock.io/<ACCESS-TOKEN>/',
    headers: {
        'Content-Type': 'application/json'
    },
    data: data
};

axios(config)
    .then(response => console.log(JSON.stringify(response.data, null, 2)))
    .catch(error => console.log(error));
```

{% endtab %}

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

```python
import requests
import json

url = "https://shared.eu-central-1.getblock.io/<ACCESS-TOKEN>/"

payload = json.dumps({
    "jsonrpc": "2.0",
    "method": "system_accountNextIndex",
    "params": [
        "5GrwvaEF5zXb26Fz9rcQpDWS57CtERHpNehXCPcNoHGKutQY"
    ],
    "id": "getblock.io"
})

headers = {
    'Content-Type': 'application/json'
}

response = requests.post(url, headers=headers, data=payload)
print(response.text)
```

{% endtab %}

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

```rust
use reqwest::Client;
use serde_json::json;

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let client = Client::new();

    let payload = json!({
        "jsonrpc": "2.0",
        "method": "system_accountNextIndex",
        "params": [
                "5GrwvaEF5zXb26Fz9rcQpDWS57CtERHpNehXCPcNoHGKutQY"
        ],
        "id": "getblock.io"
});

    let response = client
        .post("https://shared.eu-central-1.getblock.io/<ACCESS-TOKEN>/")
        .header("Content-Type", "application/json")
        .json(&payload)
        .send()
        .await?;

    let result: serde_json::Value = response.json().await?;
    println!("{:#?}", result);

    Ok(())
}
```

{% endtab %}
{% endtabs %}

## Response Example

{% code overflow="wrap" %}

```json
{
    "jsonrpc": "2.0",
    "id": "getblock.io",
    "result": 42
}
```

{% endcode %}

## Response Parameters

| Field  | Type    | Description                            |
| ------ | ------- | -------------------------------------- |
| result | integer | Next transaction nonce for the address |

## Use Cases

* Constructing the next extrinsic before signing and submitting
* Detecting account activity (counting transactions sent)
* Replacing a pending extrinsic with a higher-tip version (same nonce)

## 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)" %}
{% code overflow="wrap" %}

```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.system.accountNextIndex(...)
const result = await api.rpc.system.accountNextIndex("5GrwvaEF5zXb26Fz9rcQpDWS57CtERHpNehXCPcNoHGKutQY");
console.log(result.toHuman());

// Or use the raw RPC interface for any method:
// const raw = await api.rpc.send({ method: 'system_accountNextIndex', params: ["5GrwvaEF5zXb26Fz9rcQpDWS57CtERHpNehXCPcNoHGKutQY"] });
```

{% endcode %}
{% endtab %}

{% tab title="substrateinterface (Python)" %}
{% code overflow="wrap" %}

```python
from substrateinterface import SubstrateInterface

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

# Generic RPC call:
result = substrate.rpc_request("system_accountNextIndex", ["5GrwvaEF5zXb26Fz9rcQpDWS57CtERHpNehXCPcNoHGKutQY"])
print(result)
```

{% endcode %}
{% endtab %}
{% endtabs %}