A hash function takes input data of any size and returns a fixed-size digest (256 bits / 64 hex chars).
It is deterministic (same input = same output), one-way (cannot reverse it),
and avalanche (tiny change → completely different hash). Ethereum uses Keccak-256.
A block contains a number, nonce, data, and a prev hash.
Mining means finding a nonce so the block's SHA-256 hash starts with 0000.
Change the data — the hash breaks (turns red). Click Mine to find a valid nonce again.
Each block's prev field contains the hash of the previous block — this creates the chain.
Change data in block 1 and watch blocks 2, 3, 4, 5 all turn red. Mine block 1 first, then 2, then 3...
to rebuild the chain. This is why tampering is computationally expensive.
The blockchain is replicated across 3 peer nodes. Click any block on any node to tamper with it.
The tampered node turns red (forked). The other nodes show the canonical chain.
The network rejects the tampered version — majority wins.
Each block now records financial transactions instead of plain text. The ledger tracks balances for each participant. Transactions are validated (you can't send more than your balance) then added to the chain.
A coinbase transaction is the first transaction in every block — created by the miner/validator with no inputs.
It mints new ETH (block reward) and sends it to the validator. This is how new ETH enters circulation.
Mine the block below to claim the reward.