UUID Generator
Generate version 4 UUIDs from your browser's own cryptographic random number generator. Nothing is fetched from a server, so no one else ever sees the values.
How to use it
- Choose how many you need — anything from 1 to 100.
- Tick the format your system wants: uppercase, no hyphens, or wrapped in braces the way SQL Server and old COM code print them.
- Press Generate and copy the list. Press it again for a completely fresh set.
What a version 4 UUID actually is
A UUID is 128 bits written as 32 hexadecimal digits in five groups. Version 4 means every one of those bits is random except six: four record the version, and two record the variant. That leaves 122 random bits, which is the number that matters.
122 bits is roughly 5.3 undecillion possibilities. You could generate a billion UUIDs a second for a century and your chance of ever seeing the same one twice would still be negligible. That is why two systems that have never spoken to each other can both mint identifiers and safely assume they will not collide — no central counter, no database round trip, no coordination at all.
This page uses crypto.getRandomValues(), the browser's
cryptographic random source. It deliberately does not fall
back to Math.random(), which is fast, predictable and
completely unsuitable: if the generator is guessable then so are the
identifiers, and anything using them as a secret token is wide open.
If a browser cannot do it properly, this page says so rather than
handing you weak values that look fine.
Frequently asked questions
Are these UUIDs really unique?
Not guaranteed unique - random, which in practice is the same thing. With 122 random bits you would need to generate about 2.7 quintillion UUIDs before reaching a one in two chance of a single duplicate. Every serious system in the world relies on that, including this one.
Is it safe that they are made in my browser rather than on a server?
It is safer. A UUID from a website is a value that website has seen. These are generated by your own browser using its cryptographic random source, and nothing is sent anywhere - which matters if you are using them as tokens, invite codes or anything you would rather no one else had a copy of.
What is the difference between version 1 and version 4?
A version 1 UUID is built from the time and the machine's network card address, so it leaks when and where it was made and it sorts roughly by time. A version 4 UUID is pure randomness and leaks nothing. Unless you specifically need the ordering, version 4 is the one to use - and it is what this page makes.
Why is the thirteenth character always 4?
That digit is the version field, and 4 says this is a random UUID. The character right after the third hyphen is the variant and is always 8, 9, a or b. Those six bits are why a v4 UUID has 122 random bits rather than 128, and they are how any system can tell at a glance which kind of UUID it is holding.
Can I use a UUID as a password or an API key?
For a one-off invite link or a hard-to-guess URL, yes: 122 random bits is plenty and it is far better than anything a person would invent. For a password a human has to type, no - it is 36 characters of hex and there are better shapes for that. And never use a UUID generated by Math.random anywhere it matters, which is exactly why this page refuses to use it.
Is my text sent anywhere?
No. Everything happens in JavaScript inside your own browser. Nothing is uploaded and nothing is saved - close the tab and it is gone.