What "version 4" means

UUIDs come in several versions defined by RFC 4122, distinguished by how they're constructed — version 1 is time-and-MAC-address based, version 3/5 are derived deterministically from hashing a namespace and a name, and version 4, what this tool generates, is simply 122 random bits (6 of the 128 bits are fixed to mark the version and variant). Version 4 is the default choice for "give me a unique ID" in most modern systems because it requires no coordination, no clock, and no identifying information about the machine that generated it — unlike version 1, which historically leaked the generating machine's MAC address, a real (if usually minor) information disclosure.

Why collisions aren't a practical concern

With 122 random bits, the number of possible version-4 UUIDs is 2^122 — a number large enough that generating a billion UUIDs per second for a billion years still wouldn't give you a meaningful chance of a collision. This tool generates them with `crypto.randomUUID()`, the browser's native cryptographically-secure UUID function, rather than a hand-rolled random-string builder, so the randomness backing that guarantee is the same quality used for cryptographic keys, not a weaker PRNG.

Formatting for different targets

The canonical UUID format is lowercase with hyphens in the 8-4-4-4-12 pattern (e.g. 550e8400-e29b-41d4-a716-446655440000), and that's what most systems expect. The uppercase and no-hyphens options exist because some systems don't follow that convention — certain Windows APIs and registry contexts expect uppercase, and some database columns or URL-safe identifier schemes strip the hyphens to save 4 bytes and avoid a character some systems treat as a delimiter.