Universally unique identifiers let many machines mint IDs independently without ever coordinating or colliding. Developers use them as database primary keys, correlation IDs in distributed tracing, idempotency keys for payment APIs, and stable names for uploaded files. Pick a version, choose how many you need, and click Generate.
Two versions are offered because they suit different jobs. Version 4 is purely random, the classic choice when an identifier should reveal nothing at all. Version 7, standardised in RFC 9562, embeds a millisecond timestamp in its leading bits so IDs sort by creation time, which keeps database indexes compact. Generate anywhere from one ID to a batch of 1000, then copy the whole list or download it as a text file for seeding fixtures and test data.
Every identifier is minted by code running inside your browser tab, from values produced on your own device. No server is contacted to fetch or register IDs, nothing generated is ever transmitted or recorded, and the batch disappears when you leave the page unless you copied or downloaded it yourself.
Use v7 when the IDs will be database keys or anything you might sort or range-scan, because its embedded timestamp means new IDs cluster together and index inserts stay fast. Use v4 when the identifier should not hint at when it was created.
In practice, no. A v4 UUID contains 122 random bits, so you would need to generate roughly a billion UUIDs per second for decades before a duplicate becomes even remotely likely. For real applications you can safely treat every generated UUID as unique.
A v4 UUID reveals nothing beyond its version bits; the rest is random. A v7 UUID does encode its creation time in the first 48 bits, the very feature that makes it sortable. If exposing a creation timestamp is a concern, choose v4.