Provably fair is a cryptographic method that lets you confirm, after a game round, that the casino did not alter the outcome once your bet was placed. Three values decide everything: a server seed the casino commits to in advance, a client seed from your side, and a nonce that counts your bets. Feed those three into the verifier on this page and you can recheck any round yourself, no account and no trust required.
One thing to keep straight from the start: the proof covers the game round and nothing else. Whether the operator pays out, holds a real license or treats players fairly are separate questions that no hash can answer. Provably fair checks the math behind a result, not the casino behind the game.
Verify your bet
Enter the values from a round and the tool recalculates the result and checks that the casino did not change its server seed. Everything runs in your browser.
How this tool verifies a round
Every round rests on three values: the server seed the casino fixes in advance, the client seed from your side, and the nonce that counts each bet.
The tool runs HMAC-SHA256 with the server seed as the key and the string clientSeed:nonce:round as the message. It reads the first four bytes as a float, a decimal from 0 up to 1, then maps that float to the game's outcome.
Two checks run entirely in your browser. Seed integrity hashes the revealed server seed and compares it to the hash published before the round, so a seed swapped afterward is caught. Result recomputation rebuilds the outcome from the seeds, so a changed result is caught.
Both use the same standard functions, SHA-256 and HMAC-SHA256, as the games themselves, and nothing leaves your device. We pin the engine to known rounds and check its output matches them byte for byte, so the math you see here is the math that decided the bet.
Most provably fair games share this scheme and the same three inputs, so the same verification applies and only the final mapping changes, which is why you pick the game first. The seed-integrity check works for any site that publishes a server-seed hash. When a game uses a different hash function or mixes in seeds from other players, use the raw mode to read the underlying number and apply that game's own formula.
What is provably fair?
Provably fair means the operator commits to a random value before you bet and reveals it afterward, so you can check that the commitment held. The name is literal. Instead of asking you to believe a game is fair, the casino hands over enough data for you to prove it, one round at a time.
The concept comes out of Bitcoin gambling. Early crypto casinos had no recognizable regulator behind them, so they needed a way to demonstrate honesty that did not depend on reputation, and cryptography supplied one. That history is why provably fair gambling remains concentrated at bitcoin and crypto casinos today, and why provably fair bitcoin games like Dice and Crash ship with built-in verification far more often than studio-licensed slots.
Two common mix-ups are worth clearing away early:
- Provably fair is not the same as a certified RNG: A test lab certificate says an accredited third party has audited the game's random number generator. Provably fair removes the third party and lets you run the check yourself. The two can coexist, and they answer different questions, which the comparison further down breaks down.
- Provably fair is not blockchain verification: The math runs on ordinary hash functions in your browser or the game client. No transaction is written on-chain, and a game can be provably fair without a blockchain anywhere in sight. Platforms that do move the game logic itself into smart contracts are a separate category, which our breakdown of decentralized casinos covers.
How the provably fair algorithm works
Every provably fair algorithm rests on the same three inputs, whatever the game and whoever built it. What varies between casinos is the exact formula that turns those inputs into a result.
- Server seed: A random value the casino generates before the round. You never see it directly at first. Instead you see its hash, a fingerprint computed with a one-way function such as SHA-256. Publishing the hash pins the casino to that exact seed: change even one character later, and the fingerprint no longer matches.
- Client seed: A value contributed from your side, usually generated by your browser and editable in the game settings. Because the result depends on your seed too, the casino cannot precompute an outcome that favors the house, and setting your own string removes any doubt about who chose it.
- Nonce: A counter that starts at zero for a fresh seed pair and increases by one with every bet. It guarantees each round gets a unique result even though the two seeds stay the same across thousands of bets.
The game combines the three inputs, often by running them through HMAC-SHA256, and uses the output hash as the round's raw randomness. So the outcome of every bet is fully determined the moment the seeds and nonce are fixed, which is exactly what makes it checkable afterward.
From hash to game result
A hash is just a long hexadecimal string, so each game maps it to the numbers it needs. A typical dice implementation takes a few characters from the hash, converts them to a number and reduces it to the 0 to 100.00 betting range. A roulette version reduces the same kind of number to a pocket between 0 and 36. Card games stretch the hash further, deriving the card sequence for the whole round.
The mapping is published in each casino's fairness documentation, and implementations genuinely differ. Spribe derives round results with SHA-512, BGaming hashes a precomputed result together with a secret string using SHA-256, and many in-house originals use HMAC-SHA256 chains. That spread is why a universal verifier asks you to pick the game or platform first: the inputs are the same three values everywhere, but the formula that turns them into a dice roll is not.
Seed rotation: why the server seed stays hidden
The server seed is only revealed when you rotate to a new seed pair, never mid-cycle. The reason is simple: with the seed in hand you could compute every future nonce and know each result before betting. So the casino keeps the active seed secret, shows you its hash, and reveals the seed the moment you request a rotation and it retires.
That makes rotation the trigger for every audit. Before you rotate, all you have is the casino's word; after you rotate, you have the proof. If a casino offers no way to rotate seeds or never discloses retired server seeds, there is no way to test the fairness claim, and the label is just marketing.
How to verify a casino bet
Checking a round takes a few minutes, and you only need the game's fairness panel plus a verifier. These five steps cover the whole cycle.
Copy the server seed hash
Open the game's fairness or provably fair panel and copy the hashed server seed shown for your active seed pair.
Set your client seed
Note your client seed, or type in your own string, and check the current nonce count.
Play your rounds
Place the bets you want to audit. Each bet increases the nonce by one.
Rotate the seeds
Request a new seed pair in the fairness panel. The casino then reveals the retired server seed in plain text.
Run the verification
Hash the revealed seed and confirm it matches the pre-round hash, then recompute your results from the seeds and nonces.
Step five is where the verifier at the top of this page does the work: paste in the revealed server seed, your client seed and the nonce, and compare the recalculated result with your bet history. If the seed matches its hash and the recomputed outcome matches what the game displayed, that round is proven untouched. If the revealed seed fails its own hash, the data was altered. If only the recomputed outcome differs, first confirm the verifier is set to the right game formula, then document the mismatch with screenshots before you contact support or take a dispute further.
Provably fair games: how the proof applies per game
The seed math is identical everywhere, but what it decides differs by game. The table gives the overview, and the sections after it go deeper on the games people verify most. The wider category of crypto originals these games belong to is covered in our breakdown of casino games, including how they differ from slots and live dealer tables.
| Game | What the seeds decide | What you can verify |
|---|---|---|
| Dice | One number in the betting range per nonce | That the roll matches the seeds, and that your over/under call was settled correctly |
| Crash / Aviator | The multiplier where the round busts, fixed at takeoff | That the crash point was set before any player cashed out |
| Hi-Lo | The full card sequence for the streak | That every next card was predetermined, not dealt in response to your guess |
| Blackjack & poker | The card sequence, committed before the first deal | That hits, dealer cards and draws followed the committed sequence |
| Roulette | One pocket from 0 to 36 per spin | That the winning number came from the seeds, not from bet distribution |
| Mines | The mine layout on the grid at bet time | That the mines never moved after you started picking tiles |
| Plinko | The ball's bounce path row by row | That the path, and therefore the payout slot, was fixed at the drop |
Dice: one number per nonce
Dice is the easiest game to follow, which is why nearly every verifier supports it first. The game asks one question, whether a number lands over or under your chosen line, and the seeds plus the nonce produce exactly one number per bet, typically in a 0 to 100.00 range. Verifying a dice roll means recomputing that single number, so an audit of a hundred bets is just a hundred nonces run through the same formula. House edge on dice originals usually sits around 1%, an RTP of roughly 99%, which is also easy to sanity-check across a long session precisely because the results are recomputable.
Crash and Aviator: the multiplier is fixed at takeoff
In a crash game the multiplier looks like it climbs in real time, but the point where it busts is already fixed when the round starts, derived from the round's seed data before anyone cashes out. Your timing decides how much of the curve you capture, but it cannot move the crash point, and neither can the operator once the seed data is set.
Aviator, one of the best-known crash titles, is built by the game studio Spribe, and its fairness scheme differs from the single-player setup: the client-side half of the randomness comes from other players. Spribe combines its server seed, a random 16-character value whose hash is shown before the round, with client seeds contributed by the first players betting in that round, and derives the crash coefficient from the combined SHA-512 hash. Every round in the game history carries a fairness icon where the seeds and the resulting coefficient can be checked, so the result is verifiable even in rounds where your own seed was not among the inputs. Since the same game is licensed to every operator that carries it, the verification works identically wherever you play, though it tells you nothing about the operator itself.
Hi-Lo, blackjack and poker: the cards are fixed before the deal
Card games commit to more than a single number. In typical implementations the seed pair and nonce expand into a full shuffle, while others, like BGaming's scheme, precompute and commit the result instead; either way the order of every card is fixed before the first one is dealt. In Hi-Lo, that means the whole chain of next cards in your streak existed before your first higher-or-lower call. In provably fair blackjack, it means the dealer's hole card, your hits and every double-down draw were all sitting in a committed sequence, so the game cannot slip a bust card to you in response to how you play. Your decisions choose which cards from the sequence get revealed; they never change the sequence itself.
Verifying a card round therefore means re-deriving the committed sequence from the seed data and confirming the cards you saw appear in that exact order. Worth knowing for poker players: the technique fits house-banked games like video poker and casino hold'em, where you play against a committed deck. Peer-to-peer poker rooms, where you face other players, almost never offer this kind of proof.
Roulette: the pocket comes from the hash
Provably fair roulette maps the round's hash to a single pocket, 0 through 36 on a European layout, and the verification confirms the winning number matches the seeds. What the proof does not change is the payout structure: a straight-up win still pays 35 to 1 against 37 pockets, so the house edge of about 2.7% remains exactly what the game's rules say it is. The same logic applies to an American wheel with its extra pocket. Fairness proofs confirm the spin was random, but the house edge sits in the paytable, and that holds for every game on this page.
Provably fair casinos
Almost every crypto casino offers provably fair games, so the label alone tells you little; the useful question is which sites actually let you run the check. You can tell a genuine provably fair casino from one that merely borrowed the term with four checks, all doable before you deposit.
- The fairness documentation is public: The casino or game studio publishes how results are derived, ideally with the exact formula per game, before you ever create an account.
- The client seed is yours to set: A fairness panel that shows a client seed but never lets you change it removes the half of the proof you are supposed to control.
- Seed rotation is self-service: You can request a new seed pair whenever you want and immediately receive the retired server seed in plain text, without emailing support.
- The history is complete: Every bet lists its nonce and links to the seed data, so you can audit last week's session and not just the round you happen to have open.
The most complete verification loops tend to sit at bitcoin casinos with in-house original games, since a studio that builds its own Dice and Crash controls the whole chain from seed to result. The comparison below is every crypto casino we have reviewed, with provably fair support weighed as one factor in each site's game-selection rating, so you can set it against the license, terms and payout history that no fairness proof can vouch for.
19 casinos
Our ranking is built on our own testing, alongside independent ratings from Trustpilot and AskGamblers. Both sources update automatically, so you see both our verdict and how real players experience the casino. Every review also surfaces AskGamblers' average complaint response time.
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BlackjackDiceKenoLive CasinoMinesweeperPlinkoSlotsSports BettingKeep in mind: Provably fair is not a seal of approval. The proof covers individual game rounds, and a site can run flawless seed cryptography while still delaying withdrawals, voiding wins on technicalities or operating without a license. Check the operator with the same care you would apply to a casino with no fairness tech at all.
Provably fair vs licensed RNG testing
Provably fair verification and third-party RNG certification both target rigged outcomes, but from opposite directions, and knowing which one covers a given game tells you what you can actually check. Studio slots from major providers rely on lab audits of their random number generation, while in-house originals lean on provably fair, and some carry both. The table lines up the differences.
| Provably fair | Certified RNG testing | |
|---|---|---|
| Who runs the check | You, with the game's published seed data | An accredited test lab such as eCOGRA, iTech Labs or GLI |
| When it happens | After any round you choose, on demand | Before release and in periodic audits |
| What it proves | That a specific round followed its committed seeds | That the game's RNG produces statistically fair output over millions of rounds |
| What it cannot see | Whether the configured RTP is reasonable | Whether the specific round you just lost was tampered with |
| Where you find it | Originals such as Dice, Crash and Mines | Studio slots and table games from licensed providers |
The certificate is a statement about the game as shipped; the seed proof is a statement about your round as played. Neither says anything about whether the operator honors withdrawals, which is what casino licenses and regulator oversight exist to police.
Can a provably fair game be manipulated?
The cryptography itself has no known shortcut: a casino that has published a seed hash cannot find a different seed producing the same hash, and once you set your own client seed, it cannot have chosen your half of the input either. When the scheme is implemented honestly, the committed outcome is beyond the operator's reach. The realistic risks sit around the scheme rather than inside it.
- No commitment before the bet: If the game shows no server seed hash until after the round, the operator could generate seeds until it finds a result it likes. The pre-round hash is the entire foundation; without it there is no proof.
- A fairness panel nobody tests: The proof only binds the casino if players occasionally run it. A site whose verification page is broken, or whose revealed seeds fail their own hashes, is counting on nobody checking. Running your numbers through an independent tool rather than the casino's own widget closes that gap, which is exactly what the verifier on this page is for.
- Selective coverage: Some sites offer genuine verification on one flagship game while the rest of the library has none. The proof applies per game, never to a platform as a whole.
- A fair game with hostile terms: Nothing in the seed math stops an operator from confiscating a win under a vague bonus clause. How safe a crypto casino is is decided by its license, terms and track record, with the fairness tech as one input among several.
So the honest answer is that a correctly implemented provably fair game cannot be rigged after your bet, and the manipulation to watch for happens in the implementation and the fine print instead. Verify a few rounds whenever you start playing somewhere new, and treat any failed check as a reason to withdraw and leave.
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