How WheelSpinny picks a winner

The short version

• Every slice on the wheel has exactly the same chance of being picked.
• The result is chosen the instant you press Spin, before the wheel moves.
• The animation is steered to stop on that result. It never decides anything.
• Everything happens in your browser. No server is involved.
• You can test it yourself below, with the same code the wheel uses.

Step by step

1. Your list becomes slices. Each non-blank line is one slice. Repeated lines are separate slices, which is how you make an option more likely on purpose.
2. A random number is drawn. We ask your browser for a random number using crypto.getRandomValues, the cryptographically secure generator built into every modern browser.
3. The number becomes a slice, without bias. Turning a large random number into “one of 7 slices” with simple division would favor some slices very slightly. We use rejection sampling instead: the rare numbers that would cause that bias are thrown away and a new one is drawn, so every slice is exactly equally likely.
4. The wheel is aimed at the result. We calculate a stopping angle that puts the chosen slice under the pointer, landing somewhere inside the middle 70% of the slice so it never looks like a borderline call. The wheel then spins forward several full turns and slows to that angle.
5. The result is revealed. The winning slice is highlighted and the result pops up in words over the wheel, and screen readers announce it.

Things that don’t affect the result

• Spin length. Quick, Normal, and Long only change how long the animation takes.
• Timing. When you press Spin, or how you click, makes no difference.
• Previous spins. Each spin is independent. The same slice can win twice in a row.
• Order and color. Shuffling, sorting, slice color, or the wheel’s color palette doesn’t change any slice’s chance.

Reading the test

A fair wheel doesn’t give every slice exactly the same number of wins. Over 10,000 spins on 6 slices, a gap of 50 or so from the expected 1,667 is normal. What matters is whether the gaps are the size chance predicts, and that’s what the chi-square test measures.

The percentage it reports is how often a perfectly fair wheel would spread its wins at least as unevenly as your run did. Anything above 5% is unremarkable. Even a perfect wheel dips below 5% in about 1 run in 20, so a single low result proves nothing; a real bias would show up run after run, and more clearly with more spins. The test shows the wheel is fair over many spins. It can’t make any single spin “lucky” or “unlucky”.

How each tool picks

Every tool on WheelSpinny draws from the same secure random numbers, with the same bias-free method:

• Wheels (including the number wheel, theletter wheel, and truth or dare) pick one slice, each equally likely, as described above. The number wheel gives every number in the range one slice.
• List randomizer: a Fisher–Yates shuffle, which makes every possible order equally likely.
• Random team generator: a Fisher–Yates shuffle, then names are dealt to teams in turn. With keep-together or keep-apart rules, it deals fresh splits until one follows them all, so every split that follows the rules stays equally likely.
• Raffle winner picker: every ticket in the draw is one equal slice of the wheel, so someone with three tickets is exactly three times as likely to win as someone with one.

Where a tool animates (a spinning wheel, rows gliding into a new order), the result is always chosen first and the animation is aimed at it.

What we don’t claim

Being clear about the limits matters as much as the method:

• WheelSpinny hasn’t been independently audited or certified. It’s suitable for classrooms, games, everyday decisions, and informal draws, not for regulated lotteries, gambling, or drawings that legally require a certified process.
• The randomness comes from your browser and device. We rely on them, as every web page that uses secure random numbers does.
• In the unlikely case that a browser has no secure generator, the wheel falls back to the browser’s ordinary random function, which is fine for games but not cryptographically secure. Every current major browser has the secure generator.