Is the UUID generator free?
Yes. It is completely free to use, with no signup, no account, and no paywall.
Do I need to install anything?
No. It runs in any modern browser on desktop or mobile, with nothing to download and nothing to configure.
Does it stay local?
Yes. Generation happens entirely in your browser, and nothing is sent to a server.
Which UUID version is this, and does it matter?
Version 4, which means the identifier is essentially random: 122 random bits with 6 bits reserved to mark the version and variant. It matters a great deal for two reasons. Because it is random, it carries no information about when or where it was created, which is good for privacy and bad for database indexes. And because it is random and generated with a cryptographically secure source, it is unguessable, which means unlike a sequential integer it can safely appear in a URL you do not want enumerated.
Can two UUIDs collide?
In principle yes, in practice no. With 122 random bits, you would need to generate roughly 2.7 quintillion UUIDs before reaching a 50% chance of a single collision. To put that in perspective, generating a billion UUIDs per second, continuously, would take about 85 years to reach that probability. Every practical system treats v4 UUIDs as unique without coordination, which is the entire reason they exist: you can generate one on a laptop that is offline and be confident nobody else has it.
Why do people warn against UUIDs as database primary keys?
Because of what randomness does to a B-tree. A sequential integer key appends every new row at the right-hand edge of the index, which is cheap and keeps the tree compact. A random v4 UUID lands at an unpredictable point in the index on every insert, which causes page splits, fragments the tree, and destroys the locality that makes the buffer cache effective. On a large, write-heavy table the difference is dramatic. This is exactly the problem UUID v7 was designed to fix, by making the high bits a timestamp so inserts are ordered again.
Is a UUID a secret?
A version 4 UUID can be treated as one, which is unusual among identifier schemes. With 122 bits of cryptographically secure randomness it is not guessable or enumerable, so an unlisted URL keyed on a v4 UUID is genuinely hard to find. That is not true of v1, which encodes a MAC address and a timestamp and is therefore predictable. Even so, an unguessable URL is a weak form of access control: it leaks through browser history, referrer headers, and shared links, so it is a convenience, not authentication.
Are the UUIDs generated on a server?
No. They are generated by your browser, using crypto.randomUUID where it is available and a cryptographically secure fallback where it is not. Nothing is transmitted, and the identifiers exist only in the page until you copy them.