RNG — Random Number Generator

RNG stands for random number generator, and in programming it usually means a pseudo-random one — a deterministic algorithm seeded once. The distinction matters: a seeded PRNG is fine for a game but wrong for anything security-adjacent.

This page uses the browser's cryptographic source, which is the honest answer to 'give me a random number' without a seeded state behind it. If you are looking for how to do this in code, the developer notes below cover the two common mistakes.

How to use it

1. Set the bounds, or keep 1-100.
2. Generate as many times as you like.
3. For code, read the notes below before copying a snippet from elsewhere.

Two mistakes in almost every RNG snippet

First, `Math.floor(Math.random() * n) + 1` looks correct but uses a non-cryptographic PRNG, and for large ranges the multiplication loses precision. Second, `crypto.getRandomValues(buf); value % n` introduces modulo bias whenever n does not divide 2^32 — the first few values become slightly more likely.

The correct pattern is rejection sampling: draw a 32-bit value, discard it if it falls in the incomplete tail, and only then reduce modulo n. It costs an occasional re-draw and removes the bias entirely. In Python, `secrets.randbelow(n)` already does this; in JavaScript you have to write it yourself.

Reviewed 2026-10-21. This tool runs entirely in your browser — no server, no account, and nothing you generate is stored.