A field guide for the curious, not the crypto-bros

The internet, now with receipts.

Web3 is a way of building apps where no single company keeps the master copy. Records live on public blockchains, anyone can check them, and you hold the keys to your own stuff. This page skips the hype and shows how it actually works — with things you can click, break and fix.

Start the tour Break a blockchain
  • 6 hands-on demos
  • Real stories, real dates
  • ~10 min read
Ethereum mainnet · connecting…

Latest block

#————

Transactions
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Sealed
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Base fee
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This is real. A new block lands roughly every 12 seconds, and nobody can edit the old ones.

12sbetween Ethereum blocks
21Mbitcoins will ever exist. Hard-coded.
2009year the first Bitcoin block was mined
99.95%less energy used by Ethereum after “the Merge”

01 The shift

Read. Write. Own.

The web has had three moods. Tap through them — the difference is all about who holds the keys.

Read + Write + Own

Your stuff lives on a public ledger, tied to your key.

Balances, names and digital items are recorded on a blockchain that no single company controls. Apps become front doors to shared data instead of walled gardens. Switch apps, keep your stuff.

  • You are: a participant with a wallet.
  • Who owns it: whoever holds the private key.
  • Real example: an ENS name like vitalik.eth works across hundreds of wallets and apps — no single one can take it away.

02 Blockchain

A notebook where every page locks the one before it.

A blockchain is a list of records (blocks). Each block contains a fingerprint (hash) of the previous one. Change one old record and every fingerprint after it stops matching — so tampering is instantly obvious.

A First, meet the fingerprint

A hash turns any text into a fixed-length code. Change a single letter and the whole thing scrambles. Try it:

SHA-256 fingerprint

Try changing 5 to 6. Same function Bitcoin uses.

B Now break the chain

Each block below is valid when its hash starts with 000 and it points to the previous hash. Edit any block’s data and watch the damage spread. Then hit Mine to repair it by finding a new nonce — that’s the “work” in proof-of-work.

    03 Decentralization

    No main server. No single off switch.

    In a normal app, one company’s servers hold the truth. In a blockchain, thousands of independent computers (nodes) each keep a full copy and agree on updates. Pick a model, then start knocking computers offline.

    Click (or tap) a computer to take it offline. Click again to bring it back.

    Real story

    On 4 October 2021, a bad configuration change took Facebook, Instagram and WhatsApp offline for about six hours — billions of people, one company, one mistake. Bitcoin’s ledger, run by independent nodes around the world, has kept adding blocks since 2009.

    Network diagram of computers that can be switched off

    04 The vocabulary

    Six words you’ll hear, minus the jargon.

    Each one comes with a plain-English meaning, an everyday comparison, a real thing that happened, and the catch nobody mentions.

    How we got here, in eight moments

    1. The whitepaper

      “Satoshi Nakamoto” publishes a 9-page PDF describing peer-to-peer electronic cash.

    2. Block #0

      The Bitcoin network goes live with the genesis block.

    3. Pizza Day

      Laszlo Hanyecz pays 10,000 BTC for two pizzas — the first well-known real-world purchase.

    4. Ethereum launches

      A blockchain that can run programs, not just track coins. Smart contracts arrive.

    5. The DAO hack

      A bug drains ~3.6M ETH from an early investment DAO. The community forks the chain to undo it.

    6. CryptoKitties

      A game of breedable cartoon cats gets so popular it clogs the Ethereum network.

    7. $69 million JPEG

      Beeple’s NFT artwork sells at Christie’s, putting NFTs on the evening news.

    8. The Merge

      Ethereum switches from mining to staking, cutting its energy use by ~99.95%.

    05 Smart contracts

    A vending machine that nobody can tamper with.

    In the 1990s, computer scientist Nick Szabo compared smart contracts to vending machines: put in the right amount, get your item, no shopkeeper needed. Here’s one running step by step. Simulation · no real ETH

    1. Pick a snack

    2. Insert coins

    Sending: 0.00 ETH

    Tray is empty
    VendingMachine.sol
    contract VendingMachine {  mapping(string => uint) price;  function buy(string snack) payable {    require(msg.value >= price[snack], "Not enough ETH");    uint change = msg.value - price[snack];    payable(msg.sender).transfer(change);    emit Dispensed(msg.sender, snack);  }}

    The transaction receipt will appear here.

    Why it matters

    The rules are public code. The seller can’t quietly raise the price after you pay, and there’s no one to bribe or ask for a refund.

    Real example

    Uniswap is a set of smart contracts that swaps tokens with no company holding your money in between. It has handled well over a trillion dollars in trades.

    The catch

    Code does exactly what it says — bugs included. That’s how the 2016 DAO hack happened. “Code is law” cuts both ways.

    06 Myth-busting

    Things people get wrong. Flip to check.

    Pocket quiz

    1 / 5

    07 Try it for real

    Your wallet is your login.

    In Web3 you don’t sign up with an email and password. You connect a wallet, which holds a private key only you know. Connecting only shares your public address — it can’t move your funds.

    Connect a browser wallet

    Looking for a wallet…

    Make your own wallet — free, in 5 steps

    1. Install MetaMask only from the official site, metamask.io/download (browser extension or phone app). It costs nothing.
    2. Choose “Create a new wallet” and set a password. The password only unlocks the app on this device.
    3. Write down your 12-word Secret Recovery Phrase on paper. This is your wallet. Anyone with it owns your funds, and nobody can reset it for you.
    4. Copy your public address (it starts with 0x). That one is safe to share — it’s how people send you crypto.
    5. Come back and connect. Your wallet will be empty, and that’s fine: connecting and signing a message are both free.

    Stay safe

    • Never type your 12 or 24-word recovery phrase into any website. Ever.
    • Read every pop-up. “Sign” and “Send” are very different buttons.
    • Practice on a testnet like Sepolia — its coins are worthless, though many faucets now ask for a small real-ETH balance first.

    You now know more than most headlines.

    Web3 is still early, messy and full of both brilliant ideas and scams. The best defence is exactly what you just did: understand how it works before you put money in.

    ethereum.org — What is Web3? The original Bitcoin whitepaper Anders Brownworth’s blockchain demo