Edit a record, see its hash change, and discover how linked blocks reveal changes. An interactive educational demo with no cryptocurrency, payments or real network.
A blockchain links records using hashes. Explore a tiny library ledger, change its history, and see why the next block notices.
Use fictional text only. Edits and hashes stay in this tab. Nothing is saved. Maximum 6 blocks.
Ready. Try changing the first record.
Here, a real SHA-256 hash is computed from the block number, saved previous hash, and record text. The same input produces the same 64 hexadecimal digits. Change the input and its hash is overwhelmingly likely to change. A hash is not encryption.
Each block stores the previous block's hash. After an edit, this demo updates only the edited block's hash. The next block still refers to the old value, so the mismatch exposes the change. Later blocks inherit the broken history even if their immediate links match.
This is one editable local copy. Real blockchain networks also need rules for valid records and a way to agree on a history. Bitcoin combines independent validation with proof of work. Other blockchains can use different consensus mechanisms.
Learn more: Bitcoin Developer Guide: Blockchain · How Bitcoin works · Try Hash Playground's mining experiment