What 'provably fair' means, and how to check it
How crypto casinos let you verify every result yourself, and what that does and doesn't prove.
At a normal online casino, you trust the games are fair because an outside lab has tested them. Provably fair games go a step further: you can check each result yourself.
How it works, in plain English
Every result is made from three ingredients:
- Server seed: a secret random code from the casino. Before you play, the casino shows you a scrambled version of it, called a hash. Think of it as a sealed envelope: you can't read it, but it can't be swapped later.
- Client seed: a code from you or your browser. You can usually change it to anything you like.
- Nonce: a counter that goes up by one with every bet.
The game combines these (usually with a method called HMAC-SHA256) to produce the result. Because the casino locked in its seed before you chose yours, it can't steer the outcome.
How to check a result
- Note the hashed server seed and your client seed before you play.
- Play some rounds.
- Change ("rotate") your seed pair. The casino then reveals the old server seed.
- Check the revealed seed matches the hash you saw. Then enter the seeds and nonce into the casino's verifier, or an independent one, to recreate each result.
What it doesn't prove
Provably fair shows that a result wasn't changed after you bet. It doesn't tell you the house edge, whether the casino pays out on time, or how it treats players. Those are the things we check in our reviews.
It also usually covers only a casino's own in-house games, like dice, crash, plinko and mines. Slots and live games from big studios rely on certified random number generators instead.
18+. This guide is general information, not financial or legal advice. If gambling stops being fun, free help is here.