Random Number Generator

Where These Numbers Come From

The generator calls crypto.getRandomValues, the random source browsers expose for security work such as generating keys and tokens. It draws from the operating system’s entropy pool, which collects unpredictable physical signals: precise interrupt timings, device noise, and a hardware random instruction on most modern processors.

The alternative, Math.random, is a deterministic arithmetic formula. It produces numbers that look evenly spread and is perfectly adequate for shuffling a playlist, but it is seeded from a small amount of state, and an observer who sees enough consecutive outputs can work out that state and predict the rest. For picking a raffle winner or splitting people into teams, the cryptographic source is the better default, and it costs nothing to use.

Why a Remainder Is Not Good Enough

There is a subtle trap in turning a random 32-bit number into a number in a range like 1 to 100. The obvious approach takes the remainder: 1 + (draw % 100). That is very slightly unfair. There are 4,294,967,296 possible draws, and 100 does not divide into that evenly — it leaves a remainder of 96. The first 96 values in your range therefore have one more way of being hit than the remaining 4, so they come up marginally more often.

At a range of 100 the effect is far too small to notice. Widen the range and it grows: close to the full 32-bit span, a remainder can make some outcomes nearly twice as likely as others. This page avoids the problem with rejection sampling. It works out the largest multiple of the range that fits inside 2³² and throws away any draw at or above that ceiling, taking another one instead. Discarded draws cost a fraction of a microsecond, and every number in your range ends up genuinely equally likely.

Things This Tool Is Useful For

• Picking a winner. Number your entrants from 1 upward, set the maximum to the number of entries, and generate once.
• Drawing an order. Set the range to cover everyone, ask for as many numbers as there are people, and switch on no repeats — you get a shuffled running order rather than a list with duplicates.
• Replacing lost dice. The dice button rolls up to ten six-sided dice and totals them.
• Settling something quickly. The coin flip is one tap.

For a lottery or anything with money attached, use a properly audited draw process. This is a convenience tool with an honest random source, not a certified one.

How This Differs From the Daily Puzzle

This page is deliberately unpredictable: press generate twice and you should get different answers. The daily puzzle is the exact opposite. Its number is derived from the calendar date, so it is fixed in advance and identical for everyone playing that day — that is what makes comparing scores meaningful.

The reasoning behind that split, and what “random” actually means in each case, is covered in the explainer on random number games and fairness. If you would rather just play, the daily number game is on the home page, and the rules take about two minutes to read.