Random Number Generator

How the numbers are drawn

The range is turned into a list of equally spaced possible values — 1 to 100 is 100 values; 0 to 1 at two decimal places is 101, from 0.00 to 1.00 — and one of them is chosen with an unbiased draw from crypto.getRandomValues, the generator browsers provide for cryptography. Unbiased is the important word. The usual shortcut, taking a large random integer and the remainder after dividing by the size of the range, gives the low values a slightly bigger share whenever the range does not divide 2³² evenly. Here, random values from the incomplete final block are discarded and drawn again, so each value's chance is exactly one in the number of values.

Decimals are drawn the same way, on a grid of steps of 0.1, 0.01 and so on, and written out from that grid rather than computed as floating-point numbers — so you never see 0.30000000000000004. Both ends of the range are always included.

Repeats or no repeats, and why it matters

With repeats allowed, every draw is independent: five numbers from 1 to 10 can include 7 twice. That is right for simulating dice, sampling with replacement, or anything where one pick should not affect the next. Repeats arrive far sooner than intuition suggests — draw 23 numbers from 1 to 365 and there is a 50.7% chance that at least two match, which is the famous birthday problem.

With repeats forbidden, the numbers behave like balls drawn from a drum: once drawn, a number is out. That is what you want for raffle tickets, lottery-style picks, random seat or exam numbers, or a random sample of rows from a numbered list. Impossible requests are refused outright — ten different numbers from 1 to 5 cannot exist, and the generator says so rather than quietly returning repeats. For scale, a 6-from-49 lottery line is one of 13,983,816 equally likely combinations.

Leaving numbers out, sorting and history

The exclusion box takes single numbers and ranges — '13, 20-25, 40 to 42' — and removes them from the pool before anything is drawn. That keeps the draw exactly uniform over what is left and means it can never get stuck retrying. Use it for tickets that have already won, numbers you would rather avoid, or seats already taken. A value with more decimal places than you are drawing, such as 0.125 at two places, could never come up, so it is flagged rather than silently ignored.

Sorting changes only how the result is shown. The numbers are drawn in random order, and 'In the order drawn' keeps that order, which matters when the order means something — first prize, then second. The list of earlier draws records the time and settings of each one, so you can show what was drawn and when; it lives only in this tab and disappears when you leave the page.

Is it truly random?

Strictly, it is cryptographically secure pseudo-randomness. The browser's generator is seeded by the operating system from unpredictable sources such as hardware noise and event timing, then stretched by an algorithm designed so its output cannot be predicted or told apart from true randomness. It is the same source used to create encryption keys, and far stronger than Math.random — the generator most simple web tools use — whose future output can in principle be worked out from enough of its past output.

For anything with legal weight, such as a regulated lottery or a clinical-trial allocation, the requirement is usually an audited process rather than a particular website, so check what your rules demand. For raffles, classroom games, sampling and everyday decisions, this is as good as random gets.

Limits

Up to 10,000 numbers per draw, values up to a quadrillion (10¹⁵) in either direction, and up to six decimal places. Results of up to 300 numbers are shown individually; longer lists appear in a box you can scroll and copy. Nothing is sent anywhere — the numbers are generated in your browser, and the page keeps working offline once it has loaded.