What it does
The UUID generator makes universally unique identifiers in the standard 8-4-4-4-12 format, such as 919108f7-52d1-4320-9bac-f847db4148a8, to use as database keys, request IDs or test data:
- Version 4 (v4 random): 122 random bits.
- Version 7 (v7 time-ordered): the time it was made, then a counter and random bits, so a list of them sorts in the order they were made.
The page opens with a fresh batch: five v4 UUIDs on your first visit, then your last choices. Change an option and a new batch appears straight away.
How to use it
- Choose v4 random or v7 time-ordered.
- Set How many, from 1 to 1,000.
- Turn on Uppercase for capital letters, the way Windows shows GUIDs.
- Select Copy all for every UUID, one per line, or Copy next to a single one.
- Select Regenerate, or press Ctrl+Enter (⌘+Enter on a Mac), for a new batch with the same options.
The generator remembers your choices on this device, so they’re there the next time you open the page.
How it works
A UUID is 128 bits, written as 32 hexadecimal digits in groups of 8, 4, 4, 4 and 12. The standard, RFC 9562 from 2024, which replaced RFC 4122, sets the version digit of every UUID and limits the variant digit: the first digit of the third group is the version, 4 or 7, and the first digit of the fourth group is 8, 9, a or b, the variant bits that mark the standard’s layout.
- Version 4: the other 122 bits come from your browser’s cryptographic random number generator.
- Version 7: the first 48 bits, the first 12 digits, are the Unix time in milliseconds, so 017f22e2-79b0-… was made at 19:22:22 UTC on 22 February 2022. After the version digit, 12 bits are a counter: for each batch it starts at a random number below 2,048 and goes up by one for each UUID, so the whole batch shares one timestamp and still sorts in the order it was made. The last 62 bits are random.
Good to know
- You can make 1 to 1,000 UUIDs at a time.
- A v7 batch reads the time once, from your device’s clock, so if the clock is wrong, so is the time in the UUIDs. Different batches sort by the time each was made.
- Anyone can read the time in a v7 UUID. RFC 9562 also says not to assume UUIDs are hard to guess, and not to use them as identifiers whose possession alone grants access.
- The UUIDs come without braces or a urn:uuid: prefix; add them if your system needs them.
Privacy
Everything is made in your browser, on your device. The UUIDs aren’t uploaded or stored. Only your choices for the version, how many and Uppercase are kept, in this browser’s storage, so the page can show them again.