What is proof of work?

Proof of work requires finding an input whose hash meets a hard target, such as starting with several zeros. Because hashes are unpredictable, the only way to find one is to try many nonces, which proves real computation was spent.

A nonce is a number you change to alter the hash without changing the block data. Miners increment the nonce, rehash, and check the result, repeating until the hash satisfies the difficulty target.

How does difficulty scale?

Each additional required leading hex zero multiplies the expected work by 16, because a hex digit has 16 possible values. So three zeros take on average 16 to the power of three, about 4,096, attempts.

Which hash function does this use?

SHA-256, the same family Bitcoin uses, computed by your browser's built-in SubtleCrypto. The demo does a single SHA-256 pass rather than Bitcoin's double hash, but the principle is identical.

It is real proof-of-work in miniature: genuine SHA-256 hashing against a difficulty target. It is a learning tool, not connected to any blockchain, so it earns nothing and competes with no network.

Proof-of-Work Hash Demo

The Proof-of-Work Hash Demo lets you mine a block hash in your browser. You set the block data and a difficulty target, and the page iterates nonces with SHA-256 until it finds a hash that meets the target — exactly how proof-of-work mining works, just at a learnable scale.

How it works

A miner repeatedly hashes the block data combined with a changing nonce and checks whether the result meets a difficulty target. Here the target is a number of leading hexadecimal zeros:

attempt = SHA256( blockData + nonce )
valid   = attempt starts with N zero hex digits

Because SHA-256 output is effectively random, you cannot predict which nonce will work — you simply try nonce = 0, 1, 2, … until one succeeds. The first nonce that produces a qualifying hash is the proof of work.

Why difficulty scales by 16

Each hexadecimal digit has 16 possible values, so the chance a given digit is zero is 1/16. Requiring N leading zeros means the chance any single hash qualifies is (1/16)^N. The expected number of attempts is therefore 16^N: about 16 for one zero, 256 for two, 4,096 for three, and so on. This is why real networks raise difficulty to keep block times steady as hash power grows.

Example and notes

Mining the data hello at difficulty 4 means searching for a SHA-256 hash that begins with 0000, which takes on average 16^4 = 65,536 attempts — a fraction of a second in the browser. Push difficulty to 6 or 7 and you will feel the exponential cost first-hand. This demo runs a single SHA-256 pass locally and is not connected to any blockchain.