Provably fair,
actually verified
"Provably fair" is a claim until you check it. The check takes about thirty seconds and the tool below does the arithmetic part in your browser.
What the promise actually is
The problem provably fair solves is narrow and worth stating precisely: it proves the outcome of a round was decided before you bet, and was not altered afterwards. That is all it proves. It does not prove the odds are generous, that the house edge is small, or that the operator will pay you. Those are different questions with different answers.
How the commitment works
Before you play, the game generates a secret server seed and shows you its SHA-256 hash instead of the seed itself. A hash is one-way — you cannot work backwards from it to the seed, but any given seed always produces the same hash.
You contribute a client seed, which you can change. A nonce counts up with each round. The outcome comes from combining all three.
The trap this closes: because the server published the hash first, it is locked in. If it swapped the seed mid-round to change your result, the seed it reveals afterwards would hash to something different from what it showed you at the start. That mismatch is the entire proof.
The check only means something if you kept the hash from before you played. Copy it at the start — hashing a seed after the fact against a hash the same page just gave you proves nothing.
Verify a seed
Paste the server seed the game revealed after you rotated it. This hashes it locally in your browser — nothing is sent anywhere. Compare the result to the hash you were shown beforehand.
Rotating your seed
Changing your client seed forces the server to commit to a fresh server seed and reveal the old one. That reveal is what makes verification possible at all, so a game that never lets you rotate is not offering a check you can use.
Rotate before a session, play, rotate again at the end, then verify the seed that comes back. Doing it once tells you more than reading a hundred reviews.
What this does not cover
A round can be perfectly verifiable and still be poor value. Verification says the dice were not loaded after the throw; it says nothing about how much the house keeps on each throw. For that, work out the fair multiplier and compare — the method is on the Mines page.
Try it on a real round
Rotate your seed, play a hand, rotate again, then bring the revealed seed back here.
Play at Duel