What is a block explorer, and what can it do?

A search engine for a blockchain

Etherscan describes a block explorer as a search engine for a blockchain.¹ Anyone can use one to look up transactions, wallet addresses and smart contracts, without special software or technical knowledge.¹

You type in an address, a transaction hash or a block number, and the explorer shows what it found.⁴ Mastering Bitcoin adds that it also shows the links and flows between them.⁴

Why this works: the chain is public

Blockchains such as Ethereum and Bitcoin are public. Every transaction that has ever happened can be seen by anyone.¹ ethereum.org says Ethereum is transparent by design, so everything is verifiable.⁵

An explorer reads that public data, indexes it and organises it. It also adds extra information, such as names for well-known addresses.^6,7 So a page on an explorer mixes two things: facts from the chain, and the explorer's own additions. Lesson 4 shows why that matters.⁷

What you can look up

• A transaction, by its hash: whether it worked, who sent it, who received it and how much moved.¹
• An address: its incoming and outgoing transactions, token balances and NFTs.¹
• A block: which transactions it holds, and which validator or miner produced it.¹
• A smart contract: its code if it has been verified, its functions and its event logs.¹
• Gas prices and how busy the network is right now.¹

It only reads

An explorer can't change anything on the chain. Etherscan says it does not store your private keys and has no control over the transactions on Ethereum.¹ It does not process transactions and cannot refund them.³

So an explorer can tell you what happened. It can't undo it. Etherscan points out that successful transactions cannot be cancelled and are irreversible.³ mempool.space, a Bitcoin explorer, makes the same point about its own role: it only provides data. For help with a payment, you go to the wallet or exchange that made it.²

Use the right chain's explorer

You need an explorer that reads the chain you are checking. Here are some examples, from ethereum.org, Mastering Bitcoin and Solscan's own documentation.^5,4,8

Some explorer teams cover many chains. Etherscan says it also powers explorers for Base, BNB Chain, Polygon, Arbitrum, Solana and others.¹ Blockscout, an open-source explorer, says it supports 1,000 or more networks.⁹

The same address can exist on several chains. Etherscan's address pages link to the other chains where an address appears.¹⁰ ethereum.org's guide to revoking approvals warns that those tools only show contracts on the network you have selected.¹¹ Explorers work the same way, showing only the chains they cover: mempool.space says it only provides data about the Bitcoin network.² So always check that you are on the explorer for the chain the payment used.^2,10

Explorers for different chains also use different words. Solscan, for example, calls a transaction's ID its "signature", and shows a "slot" number for its block.¹²

A privacy warning

Looking something up is not private. Mastering Bitcoin warns that searching on an explorer may tell its operator what you are interested in. The operator can link your searches to your IP address and browser.⁴ If you look up your own transactions, the operator may be able to guess how much you hold.⁴