Provably Fair

Provably Fair is a model for generating random outcomes in online casino and crypto games in which the fairness of a result can be verified mathematically rather than taken on the operator's word. The term is used in gambling and crypto casinos, especially for games such as crash, dice, mines and plinko.

## How it works

Before a round, the server generates a server seed and publishes its hash, for example SHA-256. The player sets or receives a client seed and a nonce counter. The round result is calculated by a deterministic function of these values, usually HMAC-SHA256. After the round, the server reveals the original server seed, and the player can recalculate the hash and get the same result independently.

## Where it is used

The mechanism is most common in crypto casinos, where bets and payouts are processed on a blockchain, and in smaller operators that want to reduce audience distrust. Large licensed operators typically use certified random number generators (RNG) backed by reports from independent testing laboratories, and Provably Fair is often offered as an additional layer of transparency.

## What it affects

Provably Fair proves that the result was not changed after the bet was placed, but it does not prove that the game's underlying math is fair: RTP and house edge are set by the operator and can be anything. Therefore, verifying seeds is not the same as verifying the payout percentage.

## Common mistakes

Players confuse the server hash with the result and do not check the hash before the round begins. Operators sometimes reveal seeds without clear instructions or change the algorithm without notice. It is also important that the client seed can be changed on request, otherwise the server may prepare the outcome in advance.