Provably Fair

Yes. Every OB Original is provably fair: each result is fixed by seeds that are locked in before you bet, and nobody, us included, can change it afterwards.

Before a round you see the SHA-256 hash of our server seed, a fingerprint that can only match one seed. The other half of the result comes from your own client seed, which you can change whenever you like. Once the server seed is revealed, anyone can take the same values, repeat the calculation below and get exactly the same result.

Yes, every one. Use the Verify tool below, or the open-source script on GitHub. Each bet slip lists its seeds and nonce, with a link that fills them in for you.

Limbo turns the round's first number into a multiplier.

• Multiplier = (RTP ÷ 100) ÷ (1 − number), rounded down to two decimals.
• It's never below 1.00× and is capped at 1,000,000×.
• You win when the multiplier reaches your target.

With 99% RTP the chance of reaching a target is 99% ÷ target: 49.5% for 2×, 9.9% for 10×.

Every round's numbers come from three values:

• the server seed, made by us at random. You see its SHA-256 hash before you bet.
• the client seed, which is yours to change at any time.
• the nonce, which counts your bets: 1, 2, 3 and so on.

They're combined with HMAC-SHA256, a standard way of hashing: HMAC_SHA256(server seed, "client seed:nonce:0"). That gives 32 bytes. Every 4 bytes, divided by 2³², make a number between 0 and 1, so one hash gives eight numbers. If a round needs more, the 0 at the end becomes 1, then 2, and so on. When a game's method says "the next number", it means the next one in this list.

Some parts of a round have their own list, with a name added: "client seed:nonce:name:0". That way, one part of a round never shifts another.

When you change your seeds, the old server seed is revealed. Check that its hash matches the one you were shown, then check any round with the Verify tool below.