What Are Block Explorers and How Do They Work?

Block explorers allow anyone to view transactions on a blockchain. Here’s how they work and how to access them.

Key Takeaways:

• A block explorer is an online blockchain browser or a tool for viewing a blockchain and checking transactions.
• Block explorers exist for Bitcoin and some altcoins. 
• One of the most commonly searched forms of information on a block explorer is ‘recent blocks and transactions’.
• A Merkle tree summarises all the transactions in a block by producing a digital fingerprint of the entire set of transactions, thereby enabling users to verify whether or not a transaction was included in a block.
• Information about each individual transaction that happened in a particular block is also available.

What Are Block Explorers?

A block explorer is an online blockchain browser or a tool for viewing a blockchain and checking transactions. It provides information like the contents of an individual block, transaction history, and balance of addresses. 

In other words, a block explorer is a search tool. Like how web browsers are used to browse through the internet, block explorers allow one to browse a blockchain.

Block Explorers for Bitcoin and the Most Popular Cryptos

Block explorers exist for Bitcoin and some altcoins. To search for the transactions of a particular coin, users must use the block explorer specific to that cryptocurrency.

Popular block explorers for Bitcoin:

blockexplorer.com

blockchain.com

blockcypher.com 

btc.com

To learn more about Bitcoin, read What Is Bitcoin? A Complete Guide for Crypto Beginners.

Popular block explorers for Ethereum:

etherscan.io

ethplorer.io

blockchair.com/ethereum

We use BTC’s blockexplorer.com as an example to introduce some of the most common functions that block explorers provide. Readers may use the link above to follow our steps to navigate the blockchain.

Using Block Explorers: Finding the Latest Blocks and Unconfirmed Transactions

One of the most commonly searched forms of information on a block explorer is ‘recent blocks and transactions’. Once a miner solves a block, it is added to the blockchain, and block explorers subsequently update this information:

Using Block Explorers: Finding Blocks and Viewing All of Their Transactions

For more in-depth information for each block, users can either click the block feed link or input the block height number directly in the search box of the block explorer.

There is also information about each individual transaction that happened in a particular block. Once a user clicks into an individual transaction, its transaction ID (TXID) and the associated Bitcoin addresses are displayed. Reviewing this usually provides how many bitcoins were transacted, which address received them, and from where.

What Are Merkle Trees and Merkle Roots?

Here’s a brief introduction to what a Merkle root is and how it relates to a Merkle tree.

Merkle Trees

In Bitcoin’s blockchain system, multiple transactions exist within a block. A Merkle tree summarises all the transactions in a block by producing a digital fingerprint of the entire set of transactions, thereby enabling users to verify whether or not a transaction was included in a block.

Why Is It Called a Tree?

Technically, a Merkle tree is a tree structure constructed by hashing paired data (the leaves), then pairing and hashing the results until a single hash remains: the Merkle root. A Merkle tree is constructed from the bottom up, starting with the hashes of individual transactions (i.e., the transaction IDs). Merkle trees in Bitcoin use a double SHA-256. 

Each leaf node is a hash of transactional data, and each non-leaf node is a hash of its previous hashes. Merkle trees are binary and therefore require an even number of leaf nodes. If the number of transactions is odd, the last hash will be duplicated once to create an even number of leaf nodes.

Understanding How Merkle Trees Work

For example, imagine a block with four transactions: A, B, C, and D.

The Merkle tree is:

One idea to create a unique fingerprint for all TXIDs is concatenating all TXIDs and hashing them. However, to check whether a TXID is a part of the hash, all the other TXIDs need to be known, too.

However, with a Merkle tree, to check that a TXID is part of the Merkle root, only some of the hashes along the path of the tree need to be known. As a result, using a Merkle root as a fingerprint for the block header can indicate if a transaction exists in a block without having to know every other TXID in the block.

Using Block Explorers to Explore Further

Each piece of data displayed in block explorers is interlinked and well connected to the others. For example, from the transaction list, users can click on each transaction ID to view more details about that transaction. 

The list displays the block height in which the transaction took place, the total number of confirmations, and a few other additional data points. From there, users can click on the wallet address, navigate further, and check its transaction history and balance.

Final Words on Block Explorers

Block explorers are a key element of the trustless and decentralised nature of blockchain and cryptocurrency: anyone can publicly check which transactions were verified when. Whether new to crypto and Web3 or a seasoned trader, use this tool to make use of blockchain’s transparency.

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