How to generate UUIDs
Choose how many you need (up to 1,000), pick a version and press Generate. A fresh batch is also created whenever you change an option. Use Copy all to grab the whole list, one ID per line, ready to paste into a spreadsheet, a seed script or a test fixture.
The randomness comes from crypto.getRandomValues, the browser's cryptographically secure generator, not from Math.random. That's the same source used for generating encryption keys, so the IDs are unpredictable.
v4 or v7?
UUID v4 is 122 bits of pure randomness. It's the default almost everywhere, it reveals nothing about when or where it was created, and the chance of a collision is so small it can be ignored in practice.
UUID v7 was standardised in RFC 9562 in 2024. The first 48 bits are a millisecond timestamp and the rest is random. Because new IDs sort after older ones, they behave much better as database primary keys: inserts land at the end of a B-tree index instead of at random positions, which reduces page splits and keeps indexes compact. The trade-off is that anyone holding the ID can see roughly when it was created.
A short version of our advice: use v7 for primary keys in new tables, and v4 for anything public-facing where the creation time should stay private, such as password-reset tokens or share links. The full reasoning is in UUID v4 vs v7.
Reading a UUID
A UUID is written as 32 hex digits in five groups: 8-4-4-4-12. The first digit of the third group tells you the version. In 3f2b8c1e-9d4a-4c7e-b1f2-0a9d8e7c6b5a it's a 4. The first digit of the fourth group (8, 9, a or b) marks the standard variant.
Formatting options
Some systems want uppercase (older Microsoft tools often display GUIDs that way), and some store UUIDs as 32 characters without hyphens to save space. Both options produce the same underlying value; the hyphens and letter case are purely presentation. If you're storing UUIDs in PostgreSQL, use the native uuid type rather than text. It takes 16 bytes instead of 36 and compares faster.
Frequently asked questions
Can two generated UUIDs ever be the same?
Theoretically yes, practically no. You would need to generate around a billion v4 UUIDs every second for about 85 years to reach a 50% chance of one collision.
Is a GUID the same as a UUID?
Yes. GUID is the name Microsoft uses; the format is identical.
Are these UUIDs stored anywhere?
No. They are created in your browser and disappear when you close the page.