UUID generator

Type how many UUIDs you want, up to 500, and they appear one per line. Version picks random version 4 UUIDs or time-ordered version 7 ones; Letters and Hyphens change how they're written. They're made by your browser's cryptographic random generator and never leave your device.

To read a UUID instead, switch To to UUID details and paste it in. The decoder names its version and variant, and for the time-based versions, 1, 6 and 7, it works out when the UUID was made.

A UUID is a 128-bit number written as 32 hex digits in groups of 8, 4, 4, 4 and 12. They're also called GUIDs. The idea is that anyone can make one, anywhere, without asking anyone else, and still be sure nobody else has made the same one.

The current standard is RFC 9562, published in May 2024, which replaced RFC 4122. Four bits of every UUID say its version, and two or three bits say its variant: the 13th hex digit is the version, and the 17th starts with the variant bits.

A version 4 UUID is 122 random bits plus the 6 that mark it as version 4. It says nothing about when or where it was made, which is often exactly what you want.

A version 7 UUID starts with the time in milliseconds since 1970 and fills the rest with random bits. UUIDs made later sort after ones made earlier, which keeps database indexes tidy, but anyone holding one can see roughly when it was made.

With 122 random bits, you'd need to make about 2.7 quintillion version 4 UUIDs, 2.7 × 10¹⁸, before there's an even chance that any two of them are the same. That's the birthday problem worked out for 2¹²² possibilities, and it's why nobody checks.