# eth\_chainId - Monad

This method returns the chain ID used for signing replay-protected transactions.

## Parameters

* None

## Request

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

```bash
curl --location --request POST 'https://go.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)" %}

```javascript
import axios from 'axios';

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

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

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

{% endtab %}

{% tab title="Python" %}

```python
import requests
import json

url = "https://go.getblock.io/<ACCESS-TOKEN>/"

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

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

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

{% endtab %}

{% tab title="Rust" %}

```rust
use reqwest::header;

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let client = reqwest::Client::new();
    
    let response = client
        .post("https://go.getblock.io/<ACCESS-TOKEN>/")
        .header(header::CONTENT_TYPE, "application/json")
        .body(r#"{
            "jsonrpc": "2.0",
            "method": "eth_chainId",
            "params": [],
            "id": "getblock.io"
        }"#)
        .send()
        .await?;
    
    println!("{}", response.text().await?);
    Ok(())
}
```

{% endtab %}
{% endtabs %}

## Response

```json
{
    "jsonrpc": "2.0",
    "id": "getblock.io",
    "result": "0x8f"
}
```

## Response Parameters

| Field  | Type   | Description                                                |
| ------ | ------ | ---------------------------------------------------------- |
| result | string | The chain ID in hexadecimal. 0x8f = 143 for Monad Mainnet. |

## Monad Network Chain IDs

| Network       | Chain ID (Decimal) | Chain ID (Hex) |
| ------------- | -----------------: | -------------- |
| Monad Mainnet |                143 | 0x8f           |
| Monad Testnet |              10143 | 0x279f         |

## Use Case

The `eth_chainId` method is essential for:

* Transaction signing with replay protection
* Network verification before transactions
* Multi-chain wallet integration
* dApp network detection
* Preventing cross-chain replay attacks
* MetaMask and wallet configuration

## Error Handling

| Status Code | Error Message | Cause                            |
| ----------- | ------------- | -------------------------------- |
| 403         | Forbidden     | Missing or invalid ACCESS-TOKEN. |

## Web3 Integration

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

```javascript
import { ethers } from 'ethers';

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

const network = await provider.getNetwork();
console.log('Chain ID:', network.chainId.toString()); // 143

// Verify connected to Monad Mainnet
if (network.chainId === 143n) {
    console.log('Connected to Monad Mainnet');
}
```

{% endtab %}

{% tab title="Viem" %}

```javascript
import { createPublicClient, http } from 'viem';
import { monad } from 'viem/chains';

// Create Viem client with GetBlock
const client = createPublicClient({
  chain: monad,
  transport: http("https://go.getblock.us/<ACCESS_TOKEN>"),
});

// Using the method through Viem
async function fetchAccountViem() {
    try {
        // Method-specific Viem implementation
        const result = await client.request({
            method: 'eth_chainId',
            param: [],
        });
        console.log('Result:', result);
        return result;
    } catch (error) {
        console.error('Viem Error:', error);
        throw error;
    }
}
```

{% endtab %}
{% endtabs %}


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://docs.getblock.io/api-reference/monad-mon/eth_chainid-monad.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.