What Is a Random Number Generator?

A random number generator (RNG) is a tool or algorithm that produces numbers with no predictable pattern. Each number it returns is, in principle, independent of the ones before it, so you can't reliably guess what will come next. RNGs power everything from video games and lotteries to scientific simulations and computer security.

You can try one right now with our free Random Number Generator: set a range, choose how many numbers you want, and press Generate.

What "random" really means

In everyday language, "random" means unpredictable and unbiased. A good random number generator gives every possible value an equal and independent chance of appearing. If you generate a number between 1 and 100, each of the hundred values should be just as likely as any other, and previous results should have no influence on the next one.

The two main types of RNG

Pseudo-random number generators (PRNGs)

Most software RNGs are pseudo-random. They start from an unpredictable seed and use a mathematical formula to expand it into a long sequence that behaves like true randomness. PRNGs are fast and perfect for games, sampling, testing and everyday decisions.

True random number generators (TRNGs)

A true random number generator draws on physical, unpredictable sources such as atmospheric noise, radioactive decay or electronic thermal noise. TRNGs are slower but non-deterministic, which matters for cryptography and regulated lotteries.

Curious about the difference? Read our guide on true random vs pseudo-random.

Where random number generators are used

• Games and draws — dice rolls, card shuffles, loot drops and raffle winners.
• Security — generating passwords, tokens and cryptographic keys.
• Science and statistics — sampling, simulations and the Monte Carlo method.
• Software testing — creating varied test data to surface bugs.
• Everyday decisions — picking a winner, assigning teams or settling a tie.

How Toolssy generates random numbers

Where your browser supports it, Toolssy uses the Web Cryptography API (crypto.getRandomValues()), a cryptographically-strong source, rather than a basic Math.random() call. Everything runs locally in your browser, so your inputs and results are never sent to a server or stored. Learn more in our methodology.

Frequently asked questions

Are random number generators truly random?

Software RNGs are technically pseudo-random, but a high-quality one like the browser's crypto generator is unpredictable enough for the vast majority of uses, from games to security. Only specialised applications need a hardware true-random source.

Can I generate numbers without repeats?

Yes. Turn on the "No repeats" option in the Random Number Generator and every number in your batch will be unique.

Is it free?

Completely. Every generator on Toolssy is free, needs no account and has no usage limits.