UUID generator

Unique identifiers without asking anyone

A UUID, or universally unique identifier, is a 128-bit number written as 32 hexadecimal digits in five groups, such as 550e8400-e29b-41d4-a716-446655440000. Its purpose is to give things unique names without any central authority: any computer can generate one with an overwhelming likelihood that nobody else has ever generated the same. That makes UUIDs a standard choice for database keys, file names, session tokens, message ids, test data and anything else that needs a label that will not collide.

Version 4: random

Version 4 is made from random numbers, apart from six bits that mark the version and the variant. With 122 random bits, the chance of a collision is so small as to be irrelevant in practice: you would need to generate billions of UUIDs a second for many years for a duplicate to become likely. This tool uses your browser's cryptographically secure generator, not a predictable pseudo-random one.

Version 7: random and sortable by time

Version 7 puts the current time, in milliseconds, in its first 48 bits and fills the rest with random data. The result is still unique, but UUIDs created later sort after the ones created earlier. That is a big advantage for database primary keys, because inserting ordered keys is faster and keeps indexes compact, which is the main drawback of fully random v4 keys in large tables. Version 7 is defined in RFC 9562.

Formats

The standard form is lowercase with hyphens. Some systems want uppercase, some want the 32 digits without hyphens, and some environments, notably Microsoft ones, use braces. Tick the option you need and the whole list is formatted in one go. The nil UUID, all zeros, and the max UUID, all ones, are special values defined by the standard that are used as placeholders.

What it does not do

UUIDs are unique but not secret: they should not be used as passwords or as the only protection of a private link. It does not generate name-based versions (3 and 5) or the older time-and-MAC-address version 1, which reveals information about the machine. For random strings of your choice, use the random string generator.