How True Randomness Actually Works in a Browser-Based Generator
A cryptographically secure random number generator (the type built into modern browsers) draws from unpredictable sources of entropy specifically designed to be resistant to prediction, unlike a simple pseudo-random number generator, which produces a deterministic sequence from a starting seed value that could, in principle, be predicted if the seed were known.
Not all "random" number generation is equally unpredictable, and understanding the difference explains why some generators are suitable for security-sensitive uses and others aren't.
Simple pseudo-random generation
A basic pseudo-random number generator produces a sequence of numbers that appears random but is actually fully determined by a starting "seed" value — given the same seed, it produces the exact same sequence every time, which makes it fine for many everyday uses (like a simple game) but unsuitable for anything where genuine unpredictability matters.
Cryptographically secure generation
Modern browsers provide a cryptographically secure random number source, drawing on unpredictable system-level entropy rather than a simple predictable seed — this is the same underlying type of randomness used for generating secure passwords, and it's specifically designed to resist prediction even by someone with significant computational resources.
Why this distinction matters for different use cases
For casual uses — picking a random number for a game, shuffling a list for fun — either type works fine. For anything where predictability would be a genuine problem (drawing a winner, generating a security-relevant value), using a tool built on cryptographically secure randomness specifically matters.