ptools.io

Random Number 1 to 10

A number between one and ten, drawn when the page opens.

Runs entirely in your browser

Loading the tool…

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A number from one to ten, drawn when the page opened. Press the button for another.

Ten values means a one in ten chance of repeating the previous draw, and that is the thing to know before anybody cries foul. A run of the same number twice is unremarkable at this range and happens about every tenth press. Three in a row is one in a hundred, which is uncommon rather than impossible, and neither is evidence of anything.

Small ranges are also where the bias in a badly built generator would show. This one draws from the browser's cryptographic source and discards values that would fall in the uneven remainder rather than folding them back with a modulo, which is the usual way a "random" number ends up slightly favouring the low end.

For a wider range, change the boxes or use one to a hundred. To pick between named things rather than numbers, the wheel of names does that.

How to use it

  1. Read the number above, drawn when the page opened.
  2. Press the button for another, or change the range first.
  3. Press Copy to take the result.

Questions

Why did it give me the same number twice?

Because with ten possible values that happens about one press in ten, and every draw is independent of the last. A generator that avoided repeating itself would be the biased one: the absence of repeats is a pattern, and patterns are what randomness does not have.

Is a small range more likely to be biased?

It is where bias shows first, which is why it is worth doing properly. Taking a raw random value modulo ten favours the low end slightly, because 2^32 does not divide by ten. This draws again instead of folding the remainder, so every value is equally likely.

Is this really random?

It comes from the browser's cryptographic generator, which is seeded by the operating system from real entropy rather than from the clock. That is a stronger source than the ordinary random function most languages hand out, and far stronger than anything a person picking a number produces.

Can the result be predicted or influenced?

Not from outside. The draw happens in this tab on your own machine and no part of it is sent anywhere or fetched from anywhere, so there is nothing in the path for anyone else to see or steer. It also means the page cannot prove to a third party that a draw was fair, which matters if you are settling something contested.

Other draws

The same generator on a different range. Every one of them takes a range of your own.

Your data stays on your device

Everything above runs inside your browser as WebAssembly compiled from Rust. Nothing you type is uploaded, logged or stored on a server. You can load this page once, go offline, and it still works.

This page makes no requests at all, to anywhere. That is not a promise in the copy: it is a Content-Security-Policy header your browser enforces, and connect-src on it is none. Open the network tab and watch nothing happen.