Provably Fair — verify every result yourself
Provably fair is the cryptographic proof that a casino result wasn't rigged. Here's how the server seed, client seed and nonce work, the SHA-256 commit-reveal flow — and a live verifier that recomputes dice, coin and roulette outcomes from any seeds, right in your browser.
Enter the revealed seeds and the nonce. Your browser computes the SHA-256 hash and derives the result the same way a provably-fair game does — no server involved.
- Commit. Before you bet, the casino generates a secret server seed and shows you only its SHA-256 hash — a fingerprint it can't change later without you noticing.
- Your input. You provide (or are given) a client seed that mixes into every result, so the casino can't have pre-picked outcomes.
- Play. Each bet uses a nonce — a counter that increases by one per bet — combined with the seeds to generate that bet's result.
- Reveal. When you rotate seeds, the casino reveals the original server seed. You hash it and check it matches the fingerprint from step 1.
- Verify. You recompute every result from
server:client:nonceyourself. If they match, the game was honest — provably.
What "provably fair" actually means
On most online casinos you simply trust that the software is honest. Provably fair replaces that trust with math: every result is committed cryptographically before you bet and can be recomputed by you afterward. If the casino tried to change an outcome, the numbers wouldn't match and the cheat would be exposed. It doesn't make you win — it makes cheating detectable.
The three ingredients
Every provably-fair result is built from three values combined and hashed:
| Ingredient | Who controls it | Purpose |
|---|---|---|
| Server seed | Casino (hidden, then revealed) | The secret that's committed up front via its hash so it can't be swapped. |
| Client seed | You | Your input mixed into every result so outcomes can't be pre-arranged. |
| Nonce | Automatic | A per-bet counter (0, 1, 2, …) so each bet is unique with the same seeds. |
The game hashes something like serverSeed:clientSeed:nonce (many casinos use HMAC-SHA256 with the server seed as the key), then converts the resulting hex into a number — a dice roll from 0–100, a coin side, a roulette pocket, a crash multiplier, and so on. Our verifier above shows the base 0–1 value and a few example mappings so you can see the conversion.
How to verify a result step by step
- Copy your seeds. After rotating your server seed, the casino reveals the old one. Note the server seed, your client seed and the bet's nonce.
- Check the commit. Hash the revealed server seed with SHA-256 and confirm it equals the hashed value the casino showed you before you played.
- Recompute the result. Hash
server:client:nonce(or HMAC per the casino's stated method) and convert it exactly as the game does. - Compare. If your recomputed outcome matches what you were dealt, the bet was honest. Repeat for any nonce.
What provably fair does NOT do
Provably fair is powerful, but it's often oversold. Be clear on its limits:
- It doesn't lower the house edge. A verifiable dice game still keeps its ~1%; a verifiable Double still keeps 6.67%. Fair means honest, not profitable.
- It doesn't make you win. Randomness is still randomness — verification only proves the result wasn't tampered with.
- It only covers the game logic. It doesn't audit whether the casino pays out, holds a license, or treats deposits fairly — that's a separate question of trust.
- Slots usually aren't provably fair. Certified RNG slots (like Fortune Tiger) are lab-audited but you can't recompute each spin yourself.