A provably fair game lets you check after every bet that the casino did not change the result, using a cryptographic commitment made before you bet. The casino publishes a SHA-256 hash of a secret server seed, you add your own client seed, and the result comes from both plus a bet counter called the nonce.

The system is built from four inputs. The server seed is a long random secret chosen by the casino and kept hidden until the seeds are rotated. The hashed server seed is the SHA-256 fingerprint of that secret, shown to you before you bet, so the casino cannot change the secret later without the fingerprint changing. The client seed is your own input, which you can set yourself, so the casino cannot pick results on its own. The nonce is a counter that goes up by one with every bet, so the same seeds still give a new result each time.

Here is a worked example you can reproduce on your own computer with any HMAC-SHA256 tool. Take the server seed "example-server-seed-7f3a9c" and the client seed "my-own-seed-42", with nonce 0. Feed the message "my-own-seed-42:0:0" into HMAC-SHA256 using the server seed as the key. The digest is eba36c193a029c05b6e60eb774aa0ee047a7e2e2cb4cb9865417709d0031f79c. Take the first 4 bytes, 3,953,355,801, and divide by 2 to the power of 32. The result is u equals 0.920462. For a dice game from 1 to 100, the roll is the floor of u times 100 plus 1, which is 93. For a crash game with a 1 percent edge, the multiplier is 0.99 divided by u, which is 1.08x. The next bet, nonce 1, gives u equals 0.680221, a dice roll of 69 and a crash multiplier of 1.46x.

You can also check the commitment itself. The SHA-256 hash of the server seed "example-server-seed-7f3a9c" is 746015ab12a88fe007f7b2e6ec743902c685a40a64c137b8aa81f7b533b974e7. When the casino rotates its seeds, it reveals the old server seed. Hash it yourself: if the fingerprint matches the one you were shown before you bet, the secret was not swapped. Then rerun the HMAC calculation for any bet placed with it and confirm the result matches what you were paid.

The odds behind the game are fixed by its formula, not by the fairness check. In a crash game with a 1 percent edge, the chance of reaching at least 2x is 0.99 divided by 2, which is 49.5 percent, and the chance of reaching at least 10x is 0.99 divided by 10, which is 9.9 percent. The verification proves the draw was fixed in advance rather than edited afterwards. It does not change those odds.

That is also the limit of what provably fair proves. A dice game with a 1 percent edge is still a 1 percent edge game, and a pay table can carry any house edge and still verify perfectly. It says nothing about the casino's licence, whether a published return figure matches the table, or whether a withdrawal will be paid. It also covers only in-house crypto games such as dice, crash, limbo, plinko, mines and keno. Third-party slots and live dealer tables work differently and are not covered unless those products separately implement it.

To verify a round yourself, follow five steps: save the hashed server seed from the fairness panel before your first round; set your own client seed instead of accepting the one handed to you; play, then rotate the seed pair, which forces the old server seed to be revealed; hash the revealed seed and match it against your saved commitment; and re-derive the outcome for any bet with the published algorithm. If a site never reveals its seeds or provides no verification tool, the provably fair label is incomplete.

Q: Does provably fair mean the game has no house edge?

A: No. A provably fair dice game with a 1 percent edge is still a 1 percent edge game. The check proves the result was not changed, not that the odds are generous.

Q: Can the casino change the result after my bet?

A: No, not without breaking the commitment. The hash of the server seed was published before you bet, so any change to the secret would produce a different fingerprint.

Q: What if a site never reveals its server seed?

A: Then the provably fair label is incomplete. Without the revealed seed you cannot hash it or recompute any result, so there is nothing to verify.

Q: Which games use provably fair?

A: Mainly in-house crypto casino games such as dice, crash, limbo, plinko, mines and keno. Third-party slots and live dealer tables do not use it unless they implement it separately.