Random Picker — Roulette & Ladder

Make a fair random choice two ways: spin a roulette wheel of your options, or run a ladder draw (amidakuji, also called ghost leg) that matches people to results. The two modes answer different questions. The wheel picks one winner at a time, with equal odds for every entry however the slices look; the spin is only the animation catching up with a choice already made. The ladder assigns everyone at once and is always a one-to-one match: every person lands on a different result, which repeated spins cannot promise.

A ladder with randomly drawn rungs is not fair. Each row moves a line at most one column, so people tend to end near where they started. In a simulation with 10 people and 20 rows, the first person reached the first result 22% of the time and the last result 0.9% of the time, against 10% each for a fair draw. So this tool decides the assignment first, picking one of the n! possible assignments with equal probability, and then draws a ladder that produces it: a few rows of random rungs at the top, then the rungs that carry each line to its target (an odd-even transposition sort). It looks hand-drawn, but every person has a 1/n chance of every result.

The results start hidden behind a question mark. Tap a name and that person's path is traced in colour down to the result it reveals, or press Reveal all to see everything at once. If the number of results differs from the number of people you get a warning, and a missing result shows as a dash. Random numbers come from the browser's cryptographic generator (crypto.getRandomValues), without modulo bias. Nobody outside the screen can verify the draw afterwards, though, so for a real prize run it in front of everyone taking part.