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.

What is the Proof-of-Work Hash Demo?

Mine a SHA-256 block hash in real time by adjusting the leading-zero difficulty target. The browser iterates nonces until the hash meets the target, showing how proof-of-work mining and difficulty scaling actually work. It runs free in your browser on Gera Tools, with nothing uploaded.

Proof-of-Work Hash Demo

Name: Proof-of-Work Hash Demo
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

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.

The anatomy of a block

In this demo, the block consists of two elements: the block data (any text you enter) and the nonce (an integer the miner increments with each attempt). In a real blockchain, a block typically also contains:

A timestamp
A reference to the previous block’s hash (creating the “chain”)
A Merkle root of the transactions

The demo simplifies to just data plus nonce to isolate the proof-of-work mechanic without requiring knowledge of the full block structure.

SHA-256 and the one-way function property

SHA-256 has three properties that make proof-of-work possible:

Deterministic — the same input always produces the same output. This lets any participant verify a claimed proof by running the hash themselves.

One-way — given a hash output, you cannot reverse-engineer the input. This means the only way to find a nonce that produces a hash meeting the target is to try nonces, one after another.

Avalanche effect — changing a single bit of input changes roughly half of the output bits unpredictably. This ensures there is no shortcut: nonce N+1 gives a completely different hash from nonce N, so knowledge of one failed attempt gives no information about the next.

These three properties together mean that finding a valid nonce requires real computational work, which is the security foundation of proof-of-work consensus.

Difficulty reference table

Leading zeros required	Expected attempts	Approximate browser time
1	16	Instant
2	256	Instant
3	4,096	Instant
4	65,536	Under 1 second
5	~1 million	1–3 seconds
6	~16 million	15–45 seconds
7	~268 million	Several minutes

Times are approximate and depend on your hardware. Bitcoin’s real network currently requires hashes with around 77 leading zero bits (in binary), corresponding to difficulty in the tens of trillions — which requires specialised ASICs running in huge farms to hit the ~10-minute target block time.

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.