MotionShine01 / v4
122 random bits
The usual choice: no information inside, just randomness from crypto.getRandomValues. Two the same is not a real worry.
Free tool
UUID generator, v4, v7 and a checker.
Make UUIDs for a database, an API or a test: random version 4, or version 7, which starts with the time so the IDs sort in the order they were made. Make one or a thousand, with or without dashes, in capitals, in braces or quoted for code. Paste any UUID into the checker to see if it is valid, which version it is and, for v1, v6 and v7, when it was made.
Version 7 puts the time first, so new rows land at the end of a database index instead of all over it.
UUIDs are made in your browser with its secure random generator. Nothing is stored or sent.
Which version
Random or in time order.
02 / v7
Time first, then random
The first 48 bits are the Unix time in milliseconds (RFC 9562), so v7 IDs sort by age. IDs made in the same millisecond still come out in order.
03 / Checker
Read what is inside
Paste any UUID to see its version and variant, and the time it was made for v1, v6 and v7.
Questions
Good to know.
What is a UUID?
A 128-bit ID written as 32 hex digits in five groups, like 3f2b9c1e-8d4a-4f6b-9a2c-1e5d7b3a9f04. Anyone can make one without asking a central list, and they will not clash.
Should I use v4 or v7?
v4 when the ID should give nothing away. v7 for database keys: it sorts by time, which keeps indexes tidy, but it shows roughly when the ID was made.
What is a GUID?
Microsoft's name for the same thing. A GUID in braces, like {3f2b9c1e-...}, is a UUID; pick Braces to get that format.
Can two UUIDs be the same?
For v4 the odds are so small that it is not a practical concern. They come from your browser's secure random generator, not Math.random.
Are they saved anywhere?
No. They are made in this page and not stored or sent.