How to Read Ethereum Smart Contract Data with Etherscan and Web3.js

For newcomers, a block explorer (Block Explorer) is the most intuitive way to explore on‑chain data. The most popular Ethereum explorer is Etherscan, which lets you view transactions, blocks, and read smart‑contract state without writing code. The Sepolia testnet mirrors main‑net functionality while providing free test tokens, making it ideal for learning.

Using Etherscan to Read Contract Information

Visit Etherscan Open the Sepolia explorer at https://sepolia.etherscan.io/ .

Search the contract Paste the WETH contract address 0xFc7a5BD22dFc48565D6f04698E566Dd0C71d3155 into the search bar and press Enter.

Open the “Contract” tab Click the “Contract” tab to access the core interaction area.

Read Contract In the “Read Contract” section you can call free, read‑only functions such as name() , symbol() , and totalSupply() . Clicking a function sends a request to an Ethereum node and instantly displays the result.

Query specific information Use balanceOf(address) to check the WETH balance of any address. Enter the address and click “Query” to see the result.

This zero‑code approach is quick, visual, and requires only a web browser, making it perfect for verifying basic contract information.

Programmatic Interaction: Unlocking Powerful Data Access

When you need bulk data or want to integrate on‑chain information into an application, a script using Web3.js or Ethers.js is required.

Preparation

Node.js environment Install Node.js on your computer to run JavaScript code.

Ethereum node API Obtain a free endpoint from a provider such as QuickNode to connect to the Sepolia network.

Contract address and ABI

Contract address The WETH contract address is 0xFc7a5BD22dFc48565D6f04698E566Dd0C71d3155 .

ABI The Application Binary Interface (JSON) describes all contract functions and events; it can be copied from the “Contract” tab on Etherscan.

Using Web3.js to Query the Contract

The following Node.js script demonstrates how to read the total supply of the WETH token.

// Import web3.js library
const { Web3 } = require('web3');

// 1. Set the Ethereum node API URL (replace with your QuickNode endpoint)
const rpcURL = 'https://holy-warmhearted-bird.ethereum-sepolia.quiknode.pro/f32bd588086e3cae8b02aed4313458b1bb365323/';
const web3 = new Web3(rpcURL);

// 2. Define contract address and ABI
const contractAddress = '0xFc7a5BD22dFc48565D6f04698E566Dd0C71d3155';
const abi = [
  {
    "inputs": [],
    "name": "read",
    "outputs": [{ "internalType": "uint256", "name": "", "type": "uint256" }],
    "stateMutability": "view",
    "type": "function"
  },
  {
    "inputs": [{ "internalType": "uint256", "name": "newScore", "type": "uint256" }],
    "name": "write",
    "outputs": [],
    "stateMutability": "nonpayable",
    "type": "function"
  }
];

// 3. Create contract instance
const contract = new web3.eth.Contract(abi, contractAddress);

// 4. Call a read‑only method
async function readContractValue() {
  try {
    const value = await contract.methods.read().call();
    console.log(`Value returned from 'read' method: ${value}`);
  } catch (error) {
    console.error('Error reading contract data:', error);
  }
}

// Execute the function
readContractValue();

The script sets the RPC endpoint, creates a Web3 instance, builds a contract object with the address and ABI, and finally calls the read‑only method. The call() function indicates a gas‑free query.

Beyond simple reads, you can:

Monitor events Listen for specific contract events such as Transfer to track token movements in real time.

Batch queries Loop through many addresses to retrieve balances in a single run.

Data analysis Store retrieved data in a database for deeper analytics and visualization.

Workflow Visualization

The diagram below contrasts the manual Etherscan flow with the programmatic approach.

Summary and Outlook

Etherscan Provides a fast, visual way to verify contract data without any code.

Programmatic interaction Forms the foundation for building complex applications, performing large‑scale analysis, and creating DApps.

Start by exploring contracts on Etherscan, then set up your Node.js environment and run the sample script. As you become comfortable, you can move on to write operations, advanced transaction parsing, and building your own decentralized applications.