Provably fair verifier

Before you bet, the casino commits to a server seed by publishing its SHA-256 hash. You supply a client seed. Each bet uses an incrementing nonce. The result is HMAC-SHA256(serverSeed, clientSeed:nonce), and the first few hex characters of that output are converted into the game outcome.

Because the server seed was committed to in advance, the casino cannot change it after seeing your bet. Because you supply the client seed, it cannot have precomputed a losing sequence for you. When you rotate seeds, the old server seed is revealed and you can check every round you played against it — which is what this tool does.

What provably fair does not do is change the house edge. A verifiably fair 1% edge is still a 1% edge. It proves the casino did not cheat beyond the edge it already told you about, which is worth something, but it is not the same as the game being good value.

Implementations vary slightly between casinos — some hash the client seed as the key rather than the server seed, some use a different number of hex characters. Check your operator's own documentation if a result does not match.