How to use
Pick a version and a count (1 to 1000), then click “Generate” to create UUIDs in your browser. Turning on uppercase, no-hyphens or braces reshapes the output, and you can copy everything at once or download it as a .txt file. Paste a single UUID into the inspector below to see its version, variant, and — for v7 — the timestamp it carries.
The difference between v4 and v7
Version 4 fills all 122 non-fixed bits with cryptographically secure randomness, so nothing can be guessed from the value alone. The downside is that it has no sort order: used as a database primary key, new rows land at random positions in the index (poor locality), which causes frequent B-tree page splits and hurts cache hit rates. Version 7 stores a millisecond-precision creation timestamp in its first 48 bits, so the values themselves sort in creation order. Used as a primary key, new rows always append to the end of the index, which means fewer page splits and better cache locality. Both versions follow the RFC 9562 standard, and this tool generates the random portion with the browser’s cryptographic random function (crypto.getRandomValues).
Why it stays sorted within the same millisecond
Version 7 has 12 spare bits right after the timestamp (rand_a), and this tool increments that value for every UUID created within the same millisecond. As a result, generating several at once produces values whose plain string sort order matches the actual generation order.
How likely is a collision
Version 4 draws from a 122-bit random space, so even generating a billion per second, the odds of an accidental match are essentially zero (a birthday-problem calculation shows you’d need to generate more than 10^18 of them to reach a 50% chance of a collision). Version 7 has a smaller random portion — 74 bits — but because this tool counts up within the same millisecond, values generated in one batch never repeat.
Privacy
UUIDs are generated entirely inside your browser and are never sent to a server. Keep in mind that a v7 UUID carries its exact creation time, so use v4 instead for any value that must not reveal when it was created, such as an identifier meant to stay anonymous.