> 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/optimism-op/optimism_eth_chainid.md).

# eth\_chainId - Optimism

Example code for the eth\_chainId json-rpc method. Сomplete guide on how to use eth\_chainId json-rpc in GetBlock.io Web3 documentation.

This method returns the chain ID of the connected network. This is useful to confirm if you are connected to Optimism or not.

### Parameters

* None

### Request Sample

{% 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": "eth_chainId",
    "params": [],
    "id": "getblock.io"
}'
```

{% endtab %}

{% tab title="Javascript(axios)" %}

```bash
const axios = require('axios');

const url = "https://shared.eu-central-1.getblock.io/<ACCESS-TOKEN>/";
const headers = { "Content-Type": "application/json" };

const payload = {
    jsonrpc: "2.0",
    method: "eth_chainId",
    params: [],
    id: "getblock.io"
};

axios.post(url, payload, { headers })
    .then(response => {
        if (response.status === 200) {
            console.log("eth_chainId result:", response.data.result);
        } else {
            console.error("Error:", response.status, response.statusText);
        }
    })
    .catch(error => {
        console.error("Error:", error.response ? error.response.data : error.message);
    });
```

{% endtab %}

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

```python
import requests
import json

url = "https://shared.eu-central-1.getblock.io/<ACCESS-TOKEN>/"
headers = {
    "Content-Type": "application/json"
}
payload = {
    "jsonrpc": "2.0",
    "method": "eth_chainId",
    "params": [],
    "id": "getblock.io"
}

response = requests.post(url, headers=headers, data=json.dumps(payload))

if response.status_code == 200:
    result = response.json().get("result")
    print("eth_chainId result:", result)
else:
    print("Error:", response.status_code, response.text)
```

{% endtab %}

{% tab title="Rust" %}
{% code overflow="wrap" %}

```rs
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": "eth_chainId",
        "params": [],
        "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(())
}
```

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

### Response

A successful response returns the following:

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

### Response Parameters

* **`id`**: A unique request identifier, matching the `id` sent in the request body.
* **`jsonrpc`**: Specifies the use of JSON-RPC version 2.0.
* **`result`**: The chain ID as a hexadecimal string. `0xa` equals 10 (Optimism Mainnet).

### Use Case

The eth\_chainId method is commonly used for:

* **Transaction signing**
* **Network verification**
* **Wallet configuration**
* **Multi-chain application support**

## Web3 Integration

{% tabs %}
{% tab title="Ethers.js" %}
{% code title="Ethers.js" %}

```javascript
const { ethers } = require('ethers');

const provider = new ethers.JsonRpcProvider('https://shared.eu-central-1.getblock.io/<ACCESS-TOKEN>/');

const network = await provider.getNetwork();
console.log('Chain ID:', network.chainId); // 56n for BSC Mainnet
```

{% endcode %}
{% endtab %}

{% tab title="Viem" %}
{% code overflow="wrap" %}

```js
import { createPublicClient, http } from 'viem';
import { optimism } from 'viem/chains';

const client = createPublicClient({
    chain: optimism,
    transport: http('https://shared.eu-central-1.getblock.io/<ACCESS-TOKEN>/')
});

const chainId = await client.getChainId();
console.log('Chain ID:', chainId);
```

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