eth_chainId - zkSync

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

Returns the chain ID of the connected network. For zkSync Era mainnet the result is 0x144 (324 in decimal); for Sepolia testnet it is 0x12c (300). Chain ID is required for EIP-155 signed transactions to prevent replay attacks across chains.

Parameters

• None

Request Example

cURL

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"
}'

JavaScript (Axios)

import axios from 'axios';

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

Python (Requests)

import requests
import json

url = "https://shared.eu-central-1.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)

Rust (Reqwest)

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(())
}

Response Example

{
    "jsonrpc": "2.0",
    "id": "getblock.io",
    "result": "0x144"
}

Response Parameters

Field	Type	Description
result	string	Chain ID in hexadecimal (0x144 = 324 mainnet, 0x12c = 300 Sepolia testnet)

Use Cases

• Constructing EIP-155 signed transactions

• Validating that a wallet is connected to zkSync Era

• Multi-chain dApps that branch logic by chain ID

Error Handling

Status Code	Error Message	Cause
403	Forbidden	Missing or invalid <ACCESS-TOKEN>
-32602	Invalid params	Request parameters are missing or malformed
429	Too Many Requests	Rate limit exceeded for your plan

SDK Integration

zksync-ethers (JavaScript)

import { Provider } from 'zksync-ethers';

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

// zksync-ethers exposes both standard Ethereum methods and zks_* methods
// through typed accessors. For raw access:
const result = await provider.send('eth_chainId', []);
console.log(result);

zksync2-python (Python)

from zksync2.module.module_builder import ZkSyncBuilder

zk_web3 = ZkSyncBuilder.build('https://shared.eu-central-1.getblock.io/<ACCESS-TOKEN>/')

// zksync2-python exposes the JSON-RPC layer directly.
result = zk_web3.zksync._zks_endpoints if 'eth_chainId'.startswith('zks_') else None
# Or call any method generically:
result = zk_web3.provider.make_request('eth_chainId', [])
print(result)