Utilore

Random Number Generator

Set the range, say how many numbers you need and press the button. For a prize draw switch on «no repeats» — then no number can come up twice.

Quick picks

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Numbers come from the browser’s cryptographic source, and values from the tail of the range are discarded rather than folded back — otherwise the first numbers would come up slightly more often, which is exactly what ruins a prize draw.

How to use

  1. Enter the range, or take a ready one: 1–10, 1–100, 6 of 49.
  2. Say how many numbers to draw and whether repeats are allowed.
  3. Press «Draw» — the numbers appear in large type, easy to read out loud.
  4. The other tabs hold dice, a coin and a draw among names.

Good to know

Why not Math.random

The usual random function in a browser is fast, predictable in principle and never meant for anything that decides an outcome. Numbers here come from the cryptographic source instead — the same one that generates encryption keys. For a game it changes nothing; for a prize draw it is the difference between a draw and the appearance of one.

The discarded tail

Taking the remainder of a random number is the classic way to land in a range — and it quietly favours the first values whenever the range does not divide evenly. Over a thousand draws the bias is a fraction of a percent, which is exactly the kind of thing nobody notices and nobody can defend afterwards. Here the values from the tail are thrown away and drawn again.

Frequently asked questions

Can I use it for a giveaway?

Yes, and «no repeats» is what you want: each participant number comes up at most once. Record the screen while drawing — that is the usual way to show the audience that nothing was retried until it looked right.

How many numbers can it draw at once?

Up to a thousand with repeats, and up to the size of the range without them: asking for ten unique numbers out of five is impossible, so the result is trimmed to five rather than looping forever.

Are the numbers the same for everyone?

No. Every draw is made on your device from a fresh source, and there is no seed to share. Two people pressing the button at the same second get different numbers.

Can the range be negative?

Yes, both bounds accept negative values, and they may be given in any order — the smaller one is used as the lower bound regardless.

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