eth_chainId - Ethereum

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

This method returns the currently configured chain ID as a hex-encoded integer. Chain ID is defined by EIP-155 and is the value applications sign into transactions to prevent replay across chains. Ethereum mainnet returns 0x1, Sepolia returns 0xaa36a7, and Hoodi returns 0x88bb0.

Parameters

This method takes no parameters.

Request

cURL

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"
}'

Axios

example.js

const axios = require('axios');

const response = await axios.post('https://go.getblock.io/<ACCESS-TOKEN>/', {
    jsonrpc: '2.0',
    method: 'eth_chainId',
    params: [],
    id: 'getblock.io'
}, {
    headers: { 'Content-Type': 'application/json' }
});

console.log(response.data.result);

Request

example.py

import requests

response = requests.post(
    'https://go.getblock.io/<ACCESS-TOKEN>/',
    headers={'Content-Type': 'application/json'},
    json={
        'jsonrpc': '2.0',
        'method': 'eth_chainId',
        'params': [],
        'id': 'getblock.io'
    }
)

print(response.json())

Rust

example.rs

use reqwest::Client;
use serde_json::{json, Value};

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

Response

{
    "jsonrpc": "2.0",
    "id": "getblock.io",
    "result": "0x1"
}

Response Parameters

Parameter	Type	Description
jsonrpc	string	JSON-RPC protocol version ("2.0")
id	string	Request identifier matching the request
result	string	Hex-encoded chain ID (0x1 = Ethereum mainnet, 0xaa36a7 = Sepolia, 0x88bb0 = Hoodi)

Use Cases

• Transaction Signing: Wallets and signers include the chain ID in signed transactions per EIP-155 to prevent replay attacks across chains

• Chain-Selection Logic: dApps confirm the connected endpoint matches the intended network before initiating a write

• Multi-Chain Router Behavior: Cross-chain aggregators verify the target chain before sending calldata to the correct contract

• Wallet UX: Prompt users to switch networks when the connected chain ID doesn't match the dApp's expected chain

Error Handling

Error Code	Message	Description
-32603	Internal error	Node failed to return its configured chain ID

Web3 Integration

Ethers.js

ethers-example.js

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());  // "1" for Ethereum mainnet

Viem

viem-example.js

import { createPublicClient, http } from 'viem';
import { mainnet } from 'viem/chains';

const client = createPublicClient({
    chain: mainnet,
    transport: http('https://go.getblock.io/<ACCESS-TOKEN>/'),
});

const chainId = await client.getChainId();
console.log('Chain ID:', chainId);  // 1 for Ethereum mainnet