How does a blockchain work? Build a tiny one in your browser
Also in: Nederlands Français Español Português Deutsch Türkçe Bahasa Indonesia
A blockchain is a list of blocks where each block stores the fingerprint (hash) of the block before it. Change one letter in an old block and its fingerprint changes, which breaks every block after it. That is why history is hard to rewrite.
Step 1: the fingerprint
A hash function like SHA-256 turns any text into a fixed-length code. Change one letter and the code changes completely. You cannot work backwards from the code to the text.
Step 2: blocks linked by fingerprints
Each block holds some data, a number called the nonce, and the hash of the previous block. Because every block points to the one before, the blocks form a chain.
Step 3: mining
In proof-of-work chains like Bitcoin, a block only counts if its hash starts with a certain number of zeros. Miners try nonce after nonce until they find one. That takes work, and redoing it for many blocks takes even more.
Step 4: try to cheat
Edit an old block and you will see its hash change and every later block turn invalid. To fix it you must mine all of them again, faster than everyone else. On a big network that is practically impossible.
Solana uses a different system (proof of stake with proof of history), but the hash-linked idea is the same.
Open the Mini-Chain, type anything, mine a block, then change one letter and watch the chain break. Nothing is sent anywhere and no real coins are involved.