Free Random Number Generator (Unbiased, In-Browser)

How to generate random numbers

1. Set Min and Max — both are inclusive, so 1 to 6 covers every die face.
2. Set How many from 1 to 10,000 — values above the cap are clamped down, below 1 are clamped up.
3. Turn on Unique (no repeats) for lottery picks or sampling where each value must differ.
4. Turn on Sort ascending to return the list in order instead of draw order.
5. Press Generate, or click a preset (coin flip, D20, Powerball 5/69) to load and run canonical settings in one click.
6. Press Copy to send the comma-separated result to your clipboard.

How a secure random number generator works

There are two classes of source. A non-cryptographic PRNG like JavaScript's Math.random() is fast and deterministic from an internal seed — fine for shuffling a deck or jittering an animation, but predictable and never safe for tokens or secrets. A CSPRNG (cryptographically-strong PRNG) like crypto.getRandomValues draws from the operating system's entropy pool and resists prediction. MDN's Web Crypto reference states it directly:

"Math.random() does not provide cryptographically secure random numbers. Do not use them for anything related to security. Use the Web Crypto API instead, and more precisely the Crypto.getRandomValues() method."— MDN Web Docs, Crypto.getRandomValues()

This tool uses crypto.getRandomValues(new Uint32Array(1)) per draw. To map a raw 32-bit value into your range without skew, it computes a rejection limit and re-rolls any value at or above it:

const range = (max - min) + 1;          // inclusive
const limit = 2 ** 32 - (2 ** 32 % range);
let n;
do {
  n = crypto.getRandomValues(new Uint32Array(1))[0];
} while (n >= limit);                    // reject the skewed tail
const result = min + (n % range);        // uniform

Worked examples: settings → output

Preset reference: bounds and behaviour

The preset chips load these exact settings and run immediately. Min and max are inclusive; "unique" forbids repeats and "sorted" returns ascending order.

Frequently asked questions