Random name picker

How the pick works

Every non-empty line is one entry. The picker shuffles the whole list with the Fisher–Yates shuffle and takes the first names in the new order. Taking the first k names of a uniformly shuffled list is exactly the same, statistically, as drawing k slips out of a hat one after another without putting any back: each name has a k / n chance of being picked, and each possible set of winners is equally likely.

The random numbers behind the shuffle come from crypto.getRandomValues, the browser’s interface to the operating system’s cryptographically secure generator. It is the same source a browser uses for encryption keys, and it is not predictable from earlier outputs, unlike Math.random, which in most browsers is a fast generator designed for simulations rather than fairness. Each 32-bit value is converted to a position by rejection sampling, so no position is favoured by rounding.

A worked example

The example above draws 3 names from a list of 10. The chance that any particular person is among the three is 3 / 10 = 30%. The chance that one specific set of three is drawn, in any order, is one in 10! / (3! × 7!) = 120. If the order matters, for example first, second and third prize, there are 10 × 9 × 8 = 720 possible results, each equally likely.

Now suppose a teacher picks one pupil at random to answer each question, with everyone going back into the draw every time. With 20 pupils and 20 questions, the table shows each pupil has about a 36% chance of never being asked. That surprises people, and it is the reason to tick “remove picked names” when the aim is for everyone to get a turn: without replacement, 20 draws from 20 names reach every single person exactly once.

Draws with and without replacement

• Without replacement (tick the box): each winner leaves the list. Use it for rotas, speaking order and turn-taking, where fairness means everyone gets a go before anyone goes twice.
• With replacement (leave it unticked): every draw is from the full list. Use it when each draw is a fresh, independent event, such as a daily spot prize, and it is acceptable for the same person to win twice.

Where it stops being reliable

The mathematics of the draw is sound; the process around it is up to you. A draw on one person’s screen is only as trustworthy as that person, since they could press the button until they like the answer. For anything that matters, draw once in front of everyone. The page also does not check the list for near-duplicates such as “Sam” and “Sam B”, and every line counts, so a name pasted twice has two chances. Formal prize draws may be governed by local rules on how winners are selected and recorded; this tool does not keep the audit trail those rules may require.