Which version should I use?

Version 4 unless you have a reason. Choose version 7 when the identifier is a database key and you want inserts to stay at the end of the index, or when sorting by creation time is useful.

Can two UUIDs ever be the same?

In theory, and never in practice. A version 4 UUID has 122 random bits, so you would need to generate billions a second for decades before a collision became likely.

Is a version 7 UUID safe to show publicly?

Only if you are comfortable with people knowing when the record was created, since the timestamp is part of the value and can be read straight out of it. For anything where that leaks information, use version 4.

What is the difference between a UUID and a GUID?

Nothing, in practice. GUID is Microsoft's name for the same 128-bit identifier, which is why their tooling writes it inside braces. The braces option here produces that form.

UUID Generator

Random version 4 UUIDs, or time-ordered version 7 ones that sort by when they were made. Generate up to a thousand at a time, and check one you already have.

Runs entirely in your browser. Your files are never uploaded.

How to use UUID Generator

1Choose version 4 for random or version 7 for time-ordered.
2Set how many you need.
3Adjust the format if your system wants capitals or no hyphens.
4Copy them out.

Version 4 or version 7

Version 4 is 122 random bits. It is the right default for anything that needs to be unguessable or that will never be sorted.

Version 7 starts with the millisecond it was created, then adds randomness. That makes it sortable by creation time and, more usefully, means consecutive inserts land next to each other in a database index instead of scattering writes across it. If you are choosing a primary key for a busy table, this is the one to read about.

Where the randomness comes from

Your browser's own crypto.getRandomValues, which is the same source behind crypto.randomUUID and is suitable for security-sensitive use. Math.random is not used here at any point: it is fast, repeatable from a seed and no use at all for identifiers that must be unpredictable.

Nothing is generated on a server and nothing is logged, so a UUID you take from this page has been seen by your machine alone.

Checking one you already have

Paste a UUID into the checker and it reports the version, the variant and, for a version 7, the exact time it was generated. That last one is worth knowing before you use v7 anywhere public, since the creation time is readable by anyone holding the identifier.

Limits

A thousand at a time. Generating more in a browser tab is slower than doing it where you need them.
Two version 7 values made in the same millisecond do not sort reliably against each other.
Versions 1, 3, 5 and 6 are not offered. They need a MAC address, a namespace or a legacy layout.

Frequently asked questions

Which version should I use?: Version 4 unless you have a reason. Choose version 7 when the identifier is a database key and you want inserts to stay at the end of the index, or when sorting by creation time is useful.
Can two UUIDs ever be the same?: In theory, and never in practice. A version 4 UUID has 122 random bits, so you would need to generate billions a second for decades before a collision became likely.
Is a version 7 UUID safe to show publicly?: Only if you are comfortable with people knowing when the record was created, since the timestamp is part of the value and can be read straight out of it. For anything where that leaks information, use version 4.
What is the difference between a UUID and a GUID?: Nothing, in practice. GUID is Microsoft's name for the same 128-bit identifier, which is why their tooling writes it inside braces. The braces option here produces that form.