Provably Fair Explained: Seeds, Hashes and What They Prove
By Eoin Fahy ยท Updated 7 October 2026
A casino can use provably fair to show that it did not change a bet result after it was placed. The casino commits to its part of the result before you play, in a form that you cannot read. It reveals it after the game, and you check that it matches. It is a real protection, and narrower than the name suggests.
- 3inputs: server seed, client seed, nonce
- SHA-256the hash that locks the casino's seed
- 4.29 billionpossible values behind one result
- 0slots or live tables it applies to
The short answer
- It proves the result was fixed before you bet. The casino cannot change the outcome once it has seen your stake.
- You take part in the result. A seed you can set is mixed into every outcome, so the casino cannot pick results alone.
- It covers a casino's own games. Dice, crash, mines, plinko and similar. Slots and live tables are not provably fair.
- It does not remove the house edge. A provably fair dice game still pays back less than it takes, by a published amount.
- It only works if you check. The proof is there for anyone to run, and almost nobody does.
How provably fair works, in plain words
Think of the casino writing its half of the answer on a card and sealing it in an envelope before you make a bet. You hold the envelope. After the bet, you open it and check the card that was used to compute your result.
The envelope is a hash. A hash is a function that takes some text and yields a fixed string of characters of some other text. The same text always gives the same string, and you cannot work backwards from the string to the text. The casino reveals the hash of its secret to you, which is called the server seed. This fixes the secret without showing it to you.
Your secret is called the client seed. You can set this to any value of your choosing. The nonce, a counter that goes up by one with each bet so no two bets use the same inputs, is used along with the server and client seeds to calculate the output which decides the roll, crash or cards.
The four stages of a provably fair bet
- 1. Commit
The casino locks in its seed
It creates a server seed and shows you only its hash. Your client seed and the nonce are visible to both sides.
- 2. Bet
You play
Each bet uses the server seed, your client seed and the next nonce. Neither side can change its seed mid-bet.
- 3. Reveal
The seed is opened
When you rotate to a new seed pair, the casino shows the old server seed in full.
- 4. Verify
You check the maths
Hash the revealed seed: it must equal the hash you were shown at the start. Then recompute any bet from the three inputs.
Shuffle documents its implementation in detail. There are three inputs which go through a function called HMAC-SHA256, which produces a 32 byte output. The game takes the output four bytes at a time. Four bytes can represent 4,294,967,296 different values, which can be scaled to a dice roll or a multiplier.
How to check a provably fair bet yourself
- Open the betFind the bet in your history and open its fairness panel.
- Note the three inputsThe hashed server seed, your client seed and the nonce.
- Rotate the seed pairSet a new client seed. The old server seed is now revealed.
- Check the hashRun the revealed seed through SHA-256. It must match the hash from step 2.
- Recompute the resultUse the casino's verifier, or its published code, with the three inputs.
The step that is relevant here is step 4. The hash of the revealed seed is compared to what was provided to you prior to you placing a bet. If the hashes match, the casino is not able to swap seeds. A casino's own verifier is convenient for step 5. If you want to check a bet in a way that does not rely on the casino at all, you can either check the code that is published or use a verifier that someone else made and check it.
You are not able to verify a bet while the server seed is in use. This is by design to prevent early disclosure. Revealing it early would allow you to predict what the next result would be.
Which casino games are provably fair
Provably fair
A casino's own in-house games: dice, crash, mines, plinko, limbo, wheel and simple card games.
Some outside studios build it in too. Metaspins points to games from Spribe that can be checked from the game's own menu.
Why the result comes from one calculation the casino can publish.
Not provably fair
Slots from studios such as Pragmatic Play or Play'n GO. Live dealer tables.
Jackpots, tournaments and anything decided on a studio's own servers.
Why the casino does not produce the result, so it has nothing to commit to.
This means a crypto casino that advertises provably fair games is describing a very small part of its lobby. At most crypto casinos, a provably fair game is a few dozen titles among thousands of other games.
What provably fair cannot prove
- That the odds are good. The house edge is part of the rules. A dice game with a 1% edge is fair and still costs you 1% of everything you wager, on average.
- That the casino will pay. A verified win is worth nothing if the withdrawal is refused. Payout rules live in the terms. The hash has no say in them.
- That the casino is honest elsewhere. Bonus terms, limits and identity checks are untouched by it.
- Anything, if you never check. The system deters cheating because anyone could verify. It only catches cheating when somebody does.
- That a shared result was fair to you. In crash, one result serves every player in the round. You can verify the crash point. You cannot verify who the game was built to favour.
Provably fair answers one question well: did the casino change this result after I bet? It was never meant to answer the other ones.
Eoin Fahy, BitcoinSpinsProvably fair or an audited random number generator?
| Provably fair | Audited RNG | |
|---|---|---|
| Who checks | You, on any bet | A test lab, on a sample |
| When | After each seed is revealed | Before release, then from time to time |
| What you see | The seeds and the code | A certificate |
| Used for | In-house games | Slots, table games and live shows |
| Rests on | Maths you can repeat | Trust in the lab and the regulator |
Neither system is better in every regard. Provably fair games allow you to check results, but only for certain games. Audited games cover everything else, on someone else's word. A casino with a confirmed licence gives the audit side more weight. Crypto casino licences explained covers what regulators require.
Where to find provably fair games
- 5 of 10casinos we cover that describe provably fair games
- 1%a common house edge on in-house dice and crash
- 4%the house edge on a typical slot
- 0%of bonus wagering they count for at Betpanda
Provably fair games are described by Cloudbet, Shuffle, BC.Game, Metaspins and Betpanda on their respective websites. Shuffle and BC.Game built their versions of provably fair games in-house and brand them as Originals. Cloudbet links a Provably Fair page from its menu.
One thing to know before you play them with a bonus. Because the edge is low, casinos often exclude these games from wagering. Betpanda's welcome terms count provably fair games at 0%. Metaspins counts its Originals at 0% too.
The ten casinos are compared in full in Bitcoin casinos in Ireland.
Provably fair explained: FAQ
Are online casinos provably fair?
Only in part. A casino's own in-house games can be provably fair. Its slots and live tables come from outside studios and are not. Their fairness rests on the studio's licence and on testing by audit labs.
Can a provably fair game be rigged?
Not by changing a result after the bet, if you verify. The game can still have a house edge of any size, and a casino could build a game with poor odds. Provably fair shows that the stated rules were followed. It does not show that the rules are generous.
What is a client seed?
A string of characters that you control which is mixed into every result. The casino commits to its own seed before it knows what you control, so it can't choose a seed that aligns with the outcomes it likes.
Should I change my client seed?
Changing it has no effect on your odds, and you can change it, which means the casino isn't rigging it. You do need to change the seed pair to see the old server seed and verify past bets.
Do provably fair games have better odds?
Usually, but for a different reason. Games like dice and crash run by the casino have a house edge of about 1%, whereas a typical slot has an edge of about 4%. That comes from the game design. The provably fair system has nothing to do with it. Crypto casino rakeback shows the edge by game.
Is live casino provably fair?
No. A live table is a video stream of a real table in a studio. Nothing about it can be described by a seed and a hash. See Bitcoin live casino for how live tables are run.
Does provably fair mean a casino is safe?
No. It says nothing about whether the casino will pay you, how it treats your balance or who runs it. Are crypto casinos legit? covers those checks.
Sources
About the author
Eoin Fahy writes BitcoinSpins from Galway. He reads a casino's fairness documentation before he reads its bonus page.
Play it safe
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