Provably fair
A way of running games, mostly on crypto sites, that lets you check each result yourself using cryptography, instead of trusting a lab's report.
How it works
A provably fair game combines three inputs:
- Server seed: a random value picked by the casino. Before you bet, you're shown only its hash, a fingerprint that locks the casino into that seed without revealing it.
- Client seed: a value from your browser, which you can usually change yourself.
- Nonce: a counter that goes up by one with each bet.
The result comes from combining these in a published formula. Later, the casino reveals the plain server seed. You hash it yourself and check it matches the fingerprint you were shown, then run the formula to confirm the result. If the casino had changed the seed after seeing your bet, the hash wouldn't match.
What it proves and what it doesn't
It shows that a particular result wasn't changed after you placed your bet. It doesn't show that the game's paytable is fair, that the house edge is what the site says, or that the casino will pay out. A provably fair dice game can still have a 1% or a 5% edge built into its payouts. And it says nothing about licensing, withdrawals or how complaints are handled.
Compared with RNG certification
Traditional casinos have their random number generators tested by labs, and the regulator relies on those reports. You can't check a single spin yourself, but the whole game, including its RTP, has been tested. Provably fair lets you check one result, but often nobody independent has tested the whole game. Some sites use both.
Checking a bet yourself
- Before betting, note the hashed server seed and your client seed.
- After you rotate seeds, copy the revealed server seed.
- Use the site's verifier, or better, an independent one, to recalculate the result for each nonce.
If you never check, provably fair is only a label.
Related
18+ only. Gambling can be harmful. Set limits before you play, and see our responsible gambling guide if it stops being fun.