What is a block explorer?

A block explorer is a website or app that lets you search a blockchain's public ledger to see transactions, wallet balances, and block details. It matters because anyone can verify a payment actually happened without trusting a bank or exchange to confirm it. Say you send 0.01 BTC to a friend. You copy the transaction ID into a site like mempool.space or blockchain.com's explorer, and it shows the amount, sender and receiver addresses, how many confirmations it has, and the fee paid.

Most explorers also let you look up any wallet address to see its full history and current balance, which is why people are careful about reusing addresses if they want privacy. Ethereum has its own explorer, Etherscan, which additionally shows smart contract code and token transfers, since Ethereum tracks more than simple coin sends.