What is a UUID?
A UUID (universally unique identifier), also called a GUID, is a 128-bit number written as 32 hexadecimal digits in five groups, such as 3f2b8c1e-9d4a-4e7b-8c2f-1a6d5e9b0c34. Anyone can create one without asking a central registry, and the chance of two random UUIDs ever being the same is so small that it can be ignored.
Version 4 or version 7?
- Version 4 is 122 random bits. It reveals nothing about when or where it was made. Use it for tokens, file names and general-purpose ids.
- Version 7 starts with the time in milliseconds, followed by random bits, so ids sort in the order they were created. Databases index them faster than random ids. It is defined in RFC 9562 (2024).
How to use the UUID generator
- Pick the version and how many you need.
- Choose the format: with or without hyphens, upper case, or wrapped in braces as some Microsoft tools expect.
- Copy the list or download it as a text file, one UUID per line.
Good to know
- The random part comes from your browser’s cryptographic random number generator.
- A version 7 UUID shows when it was created, so do not use it where that would leak information.
- Upper and lower case are the same UUID; lower case is the standard form.
Frequently asked questions
Is a GUID the same as a UUID?
Yes. GUID is Microsoft’s name for the same 128-bit identifier.
Can two UUIDs ever be the same?
In theory, yes; in practice, no. You would need to generate about a billion version 4 UUIDs every second for 85 years to have a 50% chance of a single duplicate.
Can I tell when a UUID was created?
Only for time-based versions (1, 6 and 7). Paste one into “Check a UUID” to see its timestamp. Version 4 contains no time.