Weighted Random Picker

Paste a list of "label : weight" pairs and the picker draws using the cumulative-sum method against crypto.getRandomValues — so heavier options come up proportionally more often. Useful for A/B test allocation, weighted team-pairing, fair-but-biased gift exchanges, or anything where a flat coin flip would feel unfair. Toggle replacement off to draw N distinct options when you need a ranked subset.

Weights are relative, not percentages, so they need not add up to anything in particular. 3 : 1 and 75 : 25 describe the same distribution, and adding a third option changes every existing share because the denominator grows. If you want fixed percentages, keep the total at 100 yourself and the shares will read directly.

Drawing without replacement is a different distribution from drawing with it, and the difference is easy to misread. Once an option is taken it is removed and the remaining weights are renormalised, so the second draw is conditioned on the first. The consequence is that the chance of an option finishing in the top three is not its weight times three, and a heavy option is likely to be picked early but is not guaranteed a place at all. If you need a specific number of winners in fixed proportions, allocate the slots directly rather than drawing repeatedly.

The randomness comes from the browser's cryptographic generator rather than Math.random, which matters when the draw decides something people care about. It is not, however, verifiable by anyone else: nobody watching can confirm the result was not re-rolled until it looked right. For a prize draw that has to withstand suspicion, publish a commitment to the seed before drawing, or use a method every participant can check.

A short run will not look like the weights. Proportions only emerge over many draws, so a 90:10 split producing the rare option twice in a row is ordinary, not evidence of a bug.