Etherscan is the dominant block explorer for Ethereum. View any address's transaction history, token balances, contract interactions, gas spent, and approval set. Free to use, no account required for read-only access. The companion sites — Polygonscan for Polygon, Arbiscan for Arbitrum, Optimistic Etherscan for Optimism, Basescan for Base, BscScan for BNB Chain — are all run by the same team (Etherscan Pte. Ltd., Singapore-based) on the same code base.
What you can actually do with Etherscan
Five capabilities every US holder should know:
Address lookup. Paste any address into the search bar. See current ETH balance, ERC-20 token balances, NFT holdings, recent transactions, contract interactions. The starting point for any "what is this address" question.
Transaction lookup. Paste any transaction hash. See the from/to addresses, the value transferred, the gas paid, the smart-contract function called, the input data decoded, the events emitted, and the receipt status (success/revert). Essential for diagnosing failed transactions or verifying that a swap actually executed as intended.
Contract verification. If a contract's source code is uploaded to Etherscan and matches the deployed bytecode, the "Contract" tab shows the source. You can read the actual Solidity (or Vyper) the contract executes. For any contract you're about to interact with, checking that the source is verified is a basic safety step.
Approval audit (read-only). The "Token Approvals" feature lists every active ERC-20 and ERC-721 approval at an address. Same data as revoke.cash but in Etherscan's UI. Revoking happens elsewhere; reading the state happens here.
Gas tracker. Real-time view of current Ethereum gas prices, with estimates for slow / standard / fast settlement. Useful before submitting a non-urgent transaction.
The "Verified Contract" signal
When a contract's source is verified on Etherscan, the contract page displays a green checkmark and shows the actual code. Unverified contracts display only the bytecode (essentially unreadable).
For a US holder about to interact with a new DeFi protocol: check that the contract is verified. Unverified contracts are not always malicious (sometimes the developer just hasn't gotten around to uploading the source), but they are an unambiguous warning sign. Established protocols always verify; if something purports to be a new DeFi protocol with $50M TVL and is not verified, the probability of rug-pull is materially elevated.
Etherscan's API for tooling
Etherscan offers a free API tier (5 calls per second, 100,000 calls per day) that powers a huge percentage of crypto tax tools, portfolio trackers, and wallet UIs. Koinly, CoinTracker, Zerion, DeBank, Zapper — all consume the Etherscan API. The free tier requires an API key (registration with email).
For a holder running their own tooling, the API key is the entry point to building any kind of programmatic wallet monitoring. A simple script can email you when a wallet's balance changes, without needing third-party services that may go away.
What Etherscan does not show
Privacy-preserving on-chain activity (Tornado Cash deposits, certain mixer interactions) appears in Etherscan but only as the deposit/withdrawal event itself, not the linkage. For most US-resident holders this is irrelevant; for those with privacy needs, the explorer is not the right tool.
Layer-2 transactions before they finalize on L1. Arbiscan and Optimistic Etherscan show L2 transactions in real time, but the on-chain finality (when L1 confirms the L2 batch) is a separate event. For US holders moving funds between L1 and L2, the relevant explorers are the L2's own.