How it works
A UUID (also called a GUID) is a 128-bit identifier written as 32 hex digits in five groups, like 123e4567-e89b-42d3-a456-426614174000.
Version 4 UUIDs are random. The chance of two matching is so small that systems treat them as unique without checking.
The 4 at the start of the third group marks the version, and the first digit of the fourth group is 8, 9, a or b.
Good to know
Random UUIDs are not secret. Do not use them as passwords or access tokens.
In databases, random UUIDs can slow inserts on large indexed tables. Some teams use time-ordered IDs instead.
Frequently asked questions
Are these truly unique?
They are random, with 122 random bits, so a repeat is astronomically unlikely, though not strictly impossible.
What is the difference between UUID and GUID?
Nothing for practical purposes. GUID is the name used in Microsoft systems.
Can I generate them offline?
Yes. They are made in your browser, so the tool keeps working without a connection once the page has loaded.