UUID Generator
Inspect a UUID
How to use
- Choose v4 for fully random IDs or v7 for IDs that sort by creation time.
- Set how many you need, from 1 to 500, and tick Uppercase or No hyphens if your system wants them.
- Press Copy all. To check an existing UUID, paste it in the box at the bottom to see its version, variant and, for v7, when it was made.
How it works
A UUID is 128 bits written as 32 hex digits in five groups. Four bits of the third group give the version and the top bits of the fourth group give the variant, which is why a v4 always looks like xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx, where y is 8, 9, a or b.
Version 4 fills the remaining 122 bits with random numbers from your browser's cryptographic generator, so collisions are not a practical concern.
Version 7 starts with a 48-bit Unix timestamp in milliseconds, followed by random bits. IDs created later sort after earlier ones, which keeps database indexes tidy. Within a single batch, a counter keeps IDs in creation order even when several share the same millisecond.
FAQ
Should I use v4 or v7?
Use v4 when you only need a unique ID. Use v7 when the IDs become database keys, because new rows are added at the end of the index instead of scattered through it, which is faster to write and easier to sort by creation time.
Can two UUIDs ever collide?
In theory yes, in practice no. With 122 random bits in a v4, you would need to generate billions of IDs per second for decades before a repeat becomes likely.
Does a v7 UUID reveal when it was created?
Yes, anyone can read the millisecond timestamp from the first 12 hex digits. Avoid v7 for values where creation time should stay private, such as public tokens.
Are the UUIDs safe to use as secrets?
They are generated with the browser's cryptographic random source, but a UUID is meant as an identifier. Use a purpose-built token generator for passwords and API keys.