Quick answer: A provably fair game lets you check, with simple cryptography, that the casino did not change the result after you placed your bet. Before you play, the casino commits to a secret “server seed” by showing you its hash. You add your own “client seed”, and every bet uses a counter called a nonce. Later the casino reveals the server seed, so you can confirm it matches the hash and recalculate each result yourself. Provably fair does not remove the house edge, and it does not prove a casino will pay you.
Where we play provably fair games
1win is our top-rated casino (9.9/10), with thousands of slots and a crypto withdrawal that took 15 minutes in our test.
Play at 1win18+. T&Cs apply. Not available in every country. Game libraries vary, so search the lobby for provably fair games.
How provably fair works
Every provably fair system uses the same four ingredients:
| Ingredient | What it does |
|---|---|
| Server seed | A random value created by the casino. You only see its hash (a fingerprint) before you play. |
| Server seed hash | The SHA-256 hash of the server seed, shown in advance. It is the casino’s commitment: the seed can’t be changed later without the hash changing too. |
| Client seed | A value from you (or your browser). The casino can’t know it in advance, so it can’t pick a seed that beats you. |
| Nonce | A counter that goes up by one with every bet, so each bet gets a new result from the same seeds. |
The game combines the seeds and nonce, usually with HMAC-SHA256, and turns the output into a result: a dice roll, a crash point, a mines layout and so on. Because a hash can’t be reversed, you can’t work out the server seed early. And because any change to the seed would change its hash, the casino can’t swap it after seeing your bet.
How to verify a result, step by step
- Note the server seed hash shown before you play, and set your own client seed if the game allows it.
- Play your bets. Each one uses the next nonce.
- Rotate (change) your seed pair. The casino then reveals the old server seed.
- Hash the revealed server seed with a SHA-256 tool and check it matches the hash you were shown.
- Run the server seed, client seed and nonce through the game’s published formula (most casinos offer a verifier) and compare the result with what you saw in the game.
If the hash matches and the recalculated results match, the outcomes were fixed before you bet and were not altered afterwards.
How Aviator does it
In Aviator, Spribe’s server generates a seed and publishes its hash before the round. The client seeds of the first three players to bet in that round are added to it, and the combined hash sets the crash point. In the game you can open any past round to see the server seed, the client seeds and the combined hash, and check them with an independent calculator.
What provably fair does not prove
- It doesn’t remove the house edge. A game can publish every seed and still keep a built-in edge. A crash game with a 97% RTP still keeps about 3% of everything bet over time.
- It doesn’t prove the casino will pay you. Solvency, withdrawal times and bonus terms are separate questions. Check our fastest payout casinos.
- It only covers games built that way. It is common in crypto “originals” such as dice, crash, mines and plinko. Slots from studios like Pragmatic Play instead use random number generators certified by testing labs such as eCOGRA, iTech Labs or GLI.
- It doesn’t check the maths behind the formula. Verification shows results weren’t changed; it doesn’t show the game’s payout table is generous.
Provably fair vs certified RNG
| Provably fair | Certified RNG | |
|---|---|---|
| How fairness is shown | You verify each result yourself with seeds and hashes | An independent lab tests the random number generator and the game’s RTP |
| Typical games | Dice, crash, mines, plinko, limbo | Slots, table games and most branded casino content |
| Who checks | You, after each round | Testing labs, on behalf of regulators |
| House edge | Still applies | Still applies |
Where to play provably fair games
Our top-rated casino, 1win (9.9/10), offers crash games including Aviator and its own Lucky Jet, and paid our crypto withdrawal in 15 minutes. New players can use promo code Ultragambler; see our 1win promo code page. FortuneJack (9.3/10) is a long-running crypto casino with provably fair games, and paid our Bitcoin withdrawals instantly after the first one. For more options, see our best crash gambling sites.
Provably fair FAQs
What does provably fair mean?
It means you can check, using cryptographic hashes, that a game’s result was decided before you bet and was not changed afterwards.
Does provably fair mean I can win?
No. Provably fair games still have a house edge, so over time you are expected to lose a small percentage of what you bet.
How do I verify a provably fair bet?
After rotating your seeds, hash the revealed server seed and check it matches the hash shown earlier, then recalculate the result from the server seed, client seed and nonce.
Is Aviator provably fair?
Yes. Aviator combines a server seed with the client seeds of the first three players in each round, and lets you check every past round.
Are normal online slots provably fair?
Usually not. Most slots use a random number generator that is certified by an independent testing lab instead.
Important: check your local laws before you play
Online gambling laws differ from country to country, and in some places it is restricted or not permitted at all. Check that online gambling is legal where you live and that the casino accepts players from your country. You must be 18 or older (or the legal gambling age in your country, if higher). Only gamble with money you can afford to lose.
