UUID Generator

A UUID is a 128-bit value written as 32 hexadecimal digits in five dash-separated groups. The point is that anyone can generate one independently and be confident it will not collide with anyone else's — no central authority, no coordination, no round trip to a database to reserve an ID.

Version 4 fills 122 of those bits with random data, reserving six for the version and variant markers. The collision probability is famously remote: you would need to generate around a billion UUIDs per second for roughly 85 years to reach a 50% chance of a single collision. Crucially, the randomness here comes from `crypto.getRandomValues`, your browser's cryptographically secure generator — not `Math.random()`, which is fast but predictable and must never be used for identifiers that should be unguessable.

Version 7 is newer, standardised in RFC 9562 in 2024, and solves a real database problem. Because v4 values are entirely random, consecutive inserts land in random positions in a B-tree index, scattering writes across pages and fragmenting the index. v7 puts a 48-bit millisecond timestamp in the leading bits, so IDs generated later always sort after earlier ones. Inserts stay sequential, the index stays compact, and you get creation-time ordering for free. That is why v7 is now the recommended choice for database primary keys, with v4 reserved for cases where the ID must reveal nothing — password reset tokens, public-facing identifiers, anything guessable-is-dangerous.

The trade-off is exactly that: a v7 UUID leaks its creation time to anyone holding it. That is usually harmless and often useful, but it is a real disclosure and worth a moment's thought before using v7 in a public URL.

The nil UUID — all zeros — is the conventional "no value" placeholder for a UUID column that cannot be null.