Provably Fair: What the Method Commits To, and How to Check It With Your Own Hands

The commitment: why publishing a fingerprint binds the operator

A hash function takes any input and produces a fixed-length fingerprint. The same input always produces the same fingerprint; a change of one character produces a different one; and the input cannot be recovered from the fingerprint. Those three properties make a published hash a commitment: an operator that shows you the hash of its server seed before a round has fixed the seed, because any later change to the seed would produce a hash that no longer matches the one shown.

That is the whole of the idea. The game's result is computed from the server seed and inputs you can see; the operator cannot change the server seed after your bet without the published hash giving it away; and the reveal afterwards lets you check both the hash and the result. The top-ranking UK crypto casino guides each give the method a section, and the mechanism is the same at every operator that offers it.

The three inputs

• Server seed — Who sets it: The operator · When you see it: Its hash before the round; the seed itself after the reveal
• Client seed — Who sets it: You, or the game by default · When you see it: Before the round; you can change it
• Nonce — Who sets it: A counter the game increments each round · When you see it: Shown per round in the fairness panel

The server seed is the secret. The client seed is what stops the operator from choosing a server seed that produces a known sequence of results, because your seed is combined with it and you can change it at any time. The nonce is what lets one server seed serve many rounds, each with a different result, without a new commitment per round. The result of a round is a function of all three, published or linked from the fairness panel.

The check, by hand

1. Before betting, open the game's fairness panel. Note the hash of the current server seed and the current client seed. Set your own client seed if the panel allows it.
2. Play the round. Note the nonce the panel shows for it and the result you were paid.
3. Rotate the seed, or wait until the game reveals the server seed for the finished batch of rounds. Rotating forces the reveal of the old seed and the commitment of a new one.
4. Hash the revealed server seed with the function the panel names. The output must match the hash noted in step 1. If it does not, the operator changed the seed after your bet.
5. Recompute the result from the revealed server seed, your client seed and the nonce, using the formula the panel publishes or links to. The computed result must match the round you played.

Most operators provide a calculator in the fairness panel that does steps 4 and 5. Using an independent calculator once, on one round, is the only way to confirm the built-in one is honest; after that the built-in tool is a convenience. Hash functions are standard and free online tools compute them; the result formula for a dice roll is short enough to follow by hand, which makes dice the game to start with if you want to understand the mechanism before trusting it.

The leading UK guides suggest running the check at the end of each session rather than every round, and the suggestion is sensible for a player who rotates the seed at the start of each session. A changed seed shows up at the first check that follows it, so a check per session catches it; a check per round proves the same thing more often.

Which games the method reaches

• Studio slots — Built by: Third-party developers, on their servers · Provably fair: No; the studio's testing and published return figure apply
• Live dealer tables — Built by: Studios streaming real tables · Provably fair: No; physical equipment on camera and the studio's procedures apply
• In-house originals — Built by: The operator · Provably fair: Yes, where offered: crash, dice, plinko, mines, limbo and their relatives

The method reaches only games whose result is computed by the operator from seeds it controls. A studio slot's result is computed on the studio's server, and the operator cannot commit to a seed it does not hold; the studio's own testing and return figure are what apply, exactly as at a licensed casino. The originals are the family the operator builds, and the only family a player can check.

Crash, specifically. The crash point, the multiplier at which the round stops, is produced from the seeds before the round begins, so the published hash commits the operator to it in advance. A passing check proves the crash point was fixed before you staked. It does not prove that the house edge, a fixed slice of every round stated in the panel, is small, and no cash-out timing changes the expected return; the method verifies honesty, not odds.

What a passing check does not prove

1. That the house edge is reasonable. The edge is a separate stated figure, and a round can be provably fair at any edge. The check confirms the round was played as committed; the panel's edge figure says what the commitment costs.
2. Anything about studio games or live tables. The method does not reach them, and a lobby that advertises provably fair games has advertised a property of its originals alone.
3. That the operator will pay. A verifiable round at an operator with no licence in any register is a fair round you cannot collect. The Gambling Commission's report on illegal online gambling records withheld payouts among the common outcomes at unlicensed sites, and a fairness panel changes nothing about that.

The third point is why provably fair sits on our main page under the games stage and not under the licence stage. The licence decides whether a balance is paid; the method decides whether one round of one game was honest; and the two questions have different answers at most crypto operators, which are licensed outside Great Britain and owe a UK player nothing in law.

Reading a fairness panel

• Hash function named. The panel should say which standard function it uses. One that names none cannot be checked independently.
• Server seed hash shown before the round, seed shown after. Both, with a way to rotate.
• Client seed editable. A panel that lets you set your own seed is one where the operator cannot pre-select results.
• Nonce per round. Visible, incrementing.
• Result formula published or linked. Without it, step 5 of the check cannot be done independently.
• Edge stated. The figure the check does not verify, printed where you can read it.

A panel with all six is a panel the method can be run on, and the six take a minute to find. A panel missing the function name or the formula offers a calculator you have to trust, which is the thing the method exists to avoid.

The check against the route

On the main page's route, the check belongs at stage seven, playing, and it is the only stage where the player can verify the operator's work rather than rely on it. Every other stage relies on something else: stage three on a regulator's register, stage five on the network comparison, stage eight on the operator's review and the licence that bounds it.

A player who runs the check once with an independent calculator, then per session with the built-in one, has done what the method allows. A player who treats a provably fair badge as a reason to skip stage three has mistaken a property of the games for a property of the operator. You must be 18 or over to gamble in Great Britain; if gambling is causing harm, the National Gambling Helpline, run by GamCare, is free on 0808 8020 133 at any hour.

Frequently asked questions

What does provably fair mean?

That an in-house game publishes a fingerprint of its secret server seed before a round, lets you supply or see a client seed, and reveals the server seed afterwards so you can recompute the result. A match proves the round was fixed before your bet and not altered after it.

What is a hash?

A fixed-length fingerprint produced from any input by a standard function. The same input always gives the same fingerprint; a different input gives a different one; and the input cannot be worked out from the fingerprint. Publishing the hash commits the operator to the seed without revealing it.

Does provably fair apply to slots?

Not to studio slots, which run on the developer's servers under the developer's testing and published return figure. It applies to the operator's own games, crash, dice, plinko, mines and similar, where the operator offers it.

Does a passing check mean the game is fair?

It means the round was not altered after your bet. The house edge is a separate stated figure, and the check says nothing about it, about the studio games, or about whether the operator pays withdrawals.

How often should I verify?

The leading UK guides suggest at the end of each session rather than every round, which is enough to catch a changed seed. Use an independent hash calculator once, on one round, to confirm the operator's built-in tool is honest.

Can I verify on a phone?

Yes. The fairness panel and the built-in calculator run in the browser, and an independent calculator runs in a second tab. The screen is smaller; the procedure is the same.

Is a provably fair casino safer?

The method is a fairness check for one family of game and says nothing about the operator. Safety in the sense of being paid is decided by the licence, and the regulator on the card is where that is recorded.

Sources

• Gambling Commission, how we tackle illegal gambling
• Gambling Commission, organisations that can help
• Gambling Act 2005