anders94/blockchain-demo

Blockchain Demo is a simple web application for learning how blockchains work. It runs locally in a browser and lets you interact with the core concepts hands-on, rather than just reading about them. The project is paired with a YouTube video called Blockchain 101 that walks through the same ideas visually. The demo shows what a blockchain actually is: a chain of blocks where each block contains some data and a fingerprint (called a hash) that is computed from both the block's data and the fingerprint of the previous block. Because the fingerprints chain together, changing any earlier block immediately breaks every block that comes after it. This is what people mean when they describe a blockchain as an immutable ledger. The demo lets you edit block data directly so you can see the chain break in real time and understand why tampering is detectable. The demo also shows mining, the process that makes new blocks hard to add. To add a block, the software must find a number (called a nonce) that, when included in the block, produces a fingerprint starting with a specific number of zeros. Finding that number requires trying billions of guesses. The README includes a table showing how fast the difficulty grows: requiring four leading zeros takes about 15 minutes on the demo, while 21 zeros, which is roughly what the Bitcoin network requires, would take this software roughly 8 quadrillion years. Setup is straightforward: clone the repository, run npm install, and start the local server. A Docker option is also available. The difficulty level can be adjusted by editing one line in the JavaScript source. A companion repository covers public and private key cryptography as a follow-on topic.