Interactive blockchain simulator: mine blocks, add transactions, visualize hashing, and demonstrate proof-of-work concepts.
The Local Blockchain Simulator is a miniature blockchain you build in your browser. You add transactions, gather them into blocks, and mine each block by finding a nonce whose hash satisfies the current difficulty. Because every block stores the hash of the block before it, the chain is tamper-evident: change one transaction and every later block stops validating. The surprise for most users is that mining is pure trial and error, not skill: the simulator hashes the block repeatedly, varying only the nonce, until the hash happens to meet the target. Nothing here touches a real network, wallet, or currency, and nothing is uploaded.
A concrete input and expected output from the current implementation.
Input
Add a transaction: Alice pays Bob 5 coins. Then mine a block.
Expected output
The newly mined block lists the Alice-to-Bob transaction and is appended to the chain. The block also records the previous block's hash, which is what ties it to everything mined before.
A block is a bundle of transactions plus a reference to the block that came before it. Adding a transaction puts it into the next block the simulator mines, and the stored previous-hash link is what makes the chain.
To mine a block, the simulator hashes the block's contents with a number called a nonce, then checks whether the resulting hash meets the difficulty target, usually a required number of leading zeros. If it does not, the nonce increments and the block is hashed again. Difficulty sets how many zeros are required, so raising it makes the average number of attempts grow quickly, and lowering it makes blocks easier.
Each new block stores the hash of the block before it, so the blocks form a chain. Change any transaction, and that block's hash changes, which no longer matches the link stored in the next block, so every following block is flagged invalid. Repairing the chain means re-mining the altered block and each block after it, which is why rewriting a long chain costs more work than a short one.
No. Everything happens in your browser with made-up coins; there is no wallet, no network, and no value attached. It exists to show how hashing, proof of work, and block chaining work, so the numbers you see illustrate the mechanism rather than real balances.
Each nonce trial is an independent lottery. Difficulty only sets the average number of tries needed, so a given block can be solved on the first attempt or after hundreds. That variance is normal and is exactly why real networks adjust difficulty to keep block times steady.
The example and behavioral notes were checked against the browser implementation. Standards and primary references below define the relevant format, formula, or platform behavior.
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