eth_chainId - Monad

Example code for the eth_chainId JSON-RPC method. Complete guide on how to use eth_chainId JSON-RPC in GetBlock Web3 documentation.

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

Parameters

None

Request

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"
}'

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));

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)

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(())
}

Response

{
    "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

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');
}

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;
    }
}

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