UUID Generator

About this UUID generator

A UUID is a 128-bit identifier written as 32 hexadecimal digits in five groups. Version 4 (RFC 4122) fills 122 of those bits from a cryptographically secure random source — the remaining 6 bits are fixed by the version and variant fields — which is why two v4 identifiers never collide in practice. Generation here uses crypto.getRandomValues, the same CSPRNG the browser uses for keys, so the output is not predictable from previously generated values.

Version 7 (RFC 9562) is a newer layout designed for databases. The first 48 bits are a Unix timestamp in milliseconds, the next 74 are random, and the version and variant bits sit between them. Because the timestamp leads, v7 identifiers sort lexicographically in creation order, which keeps inserts into a B-tree index roughly append-only instead of scattering them the way random v4 keys do. Within the same millisecond the ordering is still random, since the remaining bits are random rather than a counter.

Two caveats. A UUID is an identifier, not a secret: v4 is unguessable but v7 embeds the creation time in cleartext, so do not use it where the time of creation is sensitive. And if you need a guaranteed sort order across a batch generated in one tick, add your own sequence number — nothing here will do that for you.