How SpinIt keeps every spin fair

The winner is chosen before the wheel starts moving. SpinIt draws a random value, maps it to one entry, and then calculates the rotation that lands that slice under the pointer.

The animation is purely visual. Frame drops, device speed, spin duration or how hard you flick the wheel cannot change which entry was already selected.

When every active entry has the same weight, each entry has an identical chance of being selected: 1 divided by the number of entries. Five entries means 20% each.

Every selection is independent. A result that has just come up is no less likely to come up again on the next spin.

In advanced mode you can give entries different weights. An entry's chance is its weight divided by the total weight of all entries.

With weights of 1, 2 and 2 the total is 5, so the chances are 20%, 40% and 40%. A heavier entry also takes a proportionally larger slice on the wheel.

Duplicate names are kept as separate entries on purpose. Each row is its own slice with its own chance of being selected.

If a name appears twice on a four-entry wheel, each row still has a 25% chance, so that name is selected 50% of the time overall.

Winner selection uses your browser's cryptographic random number generator through the Web Crypto API, not a simple pseudo-random shortcut.

Random values are drawn with rejection sampling, which removes the rounding and modulo bias that can otherwise creep in with large entry counts or large weight totals.

Everything happens locally in your browser. No server decides your result.

SpinIt is built for classroom picks, raffles, giveaways, team rotations, standups and everyday decisions.

It is not an independently audited or certified randomness service, and it is not intended for gambling, lotteries or any use where a regulator requires certified randomness.

Results depend on the browser environment it runs in. If the cryptographic generator is unavailable, SpinIt falls back to a standard random source.