What a block explorer shows you

Why anyone can read a blockchain

A public blockchain is a shared record of transactions that thousands of independent computers keep in sync. These computers are called nodes. Each full node stores a copy of the chain and checks every new block against the same rules. Nobody needs permission to run a node, and nobody needs permission to read what is inside it.

That openness is the reason this course exists. If you can read the chain, you do not have to take anyone's word for what happened. You can check for yourself whether a payment was made, when it was confirmed, which address received it and how much it cost to send.

Reading raw node data is not practical for most people, though. A node answers technical queries in formats meant for software. This is where block explorers come in.

What a block explorer is

A block explorer is a website (and usually an API) that reads data from one or more nodes, organizes it in a database and shows it as pages a person can search and follow. Think of it as a search engine and a reading room for one blockchain.

Most explorers work in three layers:

1. Nodes connected to the network receive new blocks and transactions.
2. An indexer copies that data into a database and builds lookups the node does not keep, such as "every transaction that ever touched this address".
3. A website and API turn the database into pages: a block page, a transaction page, an address page, a token page.

Well-known examples include mempool.space and Blockstream's explorer for Bitcoin, Etherscan and Blockscout for Ethereum and many EVM networks, and Solscan for Solana. IDFE is vendor-neutral: the skills in this course apply to any explorer, and you should be able to move between them without relearning anything important.

What you can search for

Almost every explorer has one search box that accepts four kinds of input:

Learning to recognize these formats on sight saves time. If someone sends you a 64-character string, it is almost certainly a transaction or block hash, not an address. One warning: an Ethereum private key is also 64 hexadecimal characters. An explorer never needs it, and anyone who asks you for yours is trying to steal from you.

A quick tour of a typical home page

When you open an explorer, the home page usually shows:

• Latest blocks: height, time since it was produced, number of transactions and who produced it (a mining pool on Bitcoin, a validator on Ethereum).
• Latest transactions: a live feed of new activity.
• Fee estimates: what it currently costs to have a transaction included quickly or slowly.
• Network statistics: for example hash rate, number of pending transactions or the average block time.
• Market price: shown by many explorers for convenience. The price is not part of the blockchain. It comes from outside market data and has nothing to do with what the chain records.

That last point matters. An explorer mixes two kinds of information: data that comes straight from the chain (blocks, transactions, balances) and data the operator adds (prices, labels such as "Exchange hot wallet", spam warnings, charts). Learn to tell them apart.

An explorer is a window, not the source of truth

The blockchain itself is the record. An explorer is someone's view of that record, and like any view it can be imperfect:

• It can lag. If the explorer's nodes or indexer fall behind, a confirmed transaction may not show up yet, or a balance may be out of date.
• It can be wrong. Software bugs and display errors happen, especially with complex transactions.
• Its labels are opinions. When an explorer tags an address as belonging to a company, that tag comes from the operator, public sources or user submissions. It is useful context, not proof.
• It can be faked. Scammers build lookalike explorer sites with fake "confirmed" pages. Always type the explorer's address yourself or use a bookmark.

Good practice follows from this. For anything important, check the same transaction on two independent explorers, or in your own wallet or node. Some explorers, such as mempool.space and Blockscout, are open source, so organizations can run their own copy against their own node and remove the dependence on a third party.

One explorer, one network

Each explorer page belongs to one specific network. A Bitcoin explorer cannot show an Ethereum transaction, and vice versa.

This gets tricky with networks that are compatible with Ethereum (often called EVM networks), such as Polygon, Arbitrum, Base or BNB Smart Chain. They all use the same 0x address format, so the same address string can exist on each of them with a completely different history and balance. If you search for an address on the wrong network's explorer, you may see an empty page and wrongly conclude that nothing happened. Before you search, always confirm which network the transaction was sent on.

What explorers cannot tell you

An explorer shows what is written on the chain. It cannot show:

• Who controls an address, unless the owner made that public or a label suggests it.
• Why a payment was made, unless the transaction carries a note or calls a contract whose purpose is clear.
• What happened off-chain, such as trades inside an exchange's own database. When you buy and sell inside a centralized exchange account, those trades usually never touch the blockchain at all.

Keeping these limits in mind will stop you from reading more into explorer data than it can support.

Exam focus: the three layers of an explorer (nodes, indexer, website/API), the four things you can search for, the difference between on-chain data and data the operator adds (prices, labels), and why you check important facts on a second explorer and on the correct network.