Provably fair is a way for a casino to prove it did not change the outcome of a bet after you placed it. It uses the same hashing maths that secures cryptocurrencies, and anyone can run the check.
The three ingredients
Server seed. A secret random string the casino generates. Before you bet, it shows you only the hash of this seed, a fingerprint that cannot be reversed.
Client seed. A string that comes from your side. You can usually change it whenever you like, which stops the casino from picking a server seed to suit a known client seed.
Nonce. A counter that goes up by one with each bet, so the same pair of seeds gives a different result every time.
How a result is produced
The casino combines the three, typically with HMAC-SHA256, and converts part of the output into the game result: a dice roll, a crash point, a card order. The exact conversion differs between casinos and games, and each casino documents its own formula.
How to verify a bet
When you rotate to a new server seed, the casino reveals the old one. Hash it and compare with the fingerprint you were shown at the start. If they match, the seed was fixed in advance. Then recompute the result from the seeds and the nonce and check it against your bet history.
Our verifier does both steps for the most common dice formula.
What it does not prove
Provably fair covers the casino's own house games. Slots and live tables from outside studios rely on certification from testing labs instead.
It also says nothing about whether you will be paid. A fair roll is no use if the withdrawal never arrives, which is why we test withdrawals separately.
