UUID Generator

What a UUID is

A UUID is a 128-bit identifier written as 36 characters with hyphens. Its key property: a value can be created anywhere, even on a phone with no network, and it will almost certainly never collide with one created somewhere else.

No shared counter is needed because of this. Two systems can create records independently, and neither has to ask a database for the next number.

Versions 1 through 5 are defined in RFC 4122, and versions 6, 7 and 8 were added by RFC 9562. The tool generates values by these rules.

Which version to pick

• v4: random bits, the usual choice for record identifiers;
• v7: the first 48 bits hold a timestamp, so values sort in order of creation. This is what people put into primary keys of new databases;
• v1: time plus node, needed when an older system requires it;
• v5 and v3: derived from a namespace and a name, so the same name always produces the same UUID;
• nil: all zeros, meaning "no identifier".