Provably fair, explained

Provably fair lets you check that a round’s result was fixed before you bet and was not changed afterwards. It does not make a game fair in the everyday sense, and it does not make results predictable.

How it works

Commit. The server picks a secret server seed and shows you only its SHA-256 hash, a fingerprint that cannot be reversed.
Your input. You (or other players) supply a client seed, so the server cannot choose a result that suits it after seeing your bet.
Play. Each round’s result is computed from both seeds and a round counter (the nonce).
Reveal and verify. Later the server reveals its seed. Anyone can hash it, compare the hash with the fingerprint shown earlier, and recompute every round.

Try it

A textbook scheme: crash point from HMAC-SHA256(server seed, “client seed:nonce”), 97% RTP. It shows the idea; it is not the algorithm of any particular game.

Fingerprint (SHA-256), shown before any round:
—

2. Your client seed

Revealed server seed:

5. Seed to verify (try changing one character)

What provably fair proves

The result of each round was fixed before the round and not changed after your bet.
The published algorithm was actually used to produce it.

What it does not prove

That the game runs at the RTP you expect: the RTP is part of the algorithm and can be set lower.
That the site is licensed in your country, pays out, or treats players fairly. A site can be provably fair and still unlicensed.
That anyone can predict the next round. Without the secret seed the result cannot be computed, and the hash cannot be reversed: guessing a 256-bit seed is not feasible. See why predictors are scams.

Checking a real game

Use the game’s own verification screen or data. Aviator, for example, shows the seeds and hash for past rounds in its provably fair menu. Our demo uses a generic scheme and cannot verify a specific provider’s rounds.