What is a UUID?

A UUID (Universally Unique Identifier) is a 128-bit value written as 36 characters, such as 3f2504e0-4f89-41d3-9a0c-0305e82c3301. It is designed so that anyone can generate one independently without coordinating with a central authority, and still not collide with anyone else's.

What is a version 4 UUID?

Version 4 UUIDs are generated from random data rather than from a timestamp or hardware address. That makes them the right choice when you do not want the identifier to leak when or where it was created.

Can two UUIDs ever be the same?

In theory yes, in practice no. A v4 UUID has 122 random bits, giving about 5.3 x 10^36 possibilities. You would need to generate billions per second for many years before a collision became likely.

Are these UUIDs cryptographically secure?

Yes. They use crypto.getRandomValues(), your browser's cryptographically secure random source, rather than Math.random(). That matters if the identifier must be unguessable, such as a share link or session token.

Should I use a UUID as a database primary key?

It depends. UUIDs let you generate ids on the client and merge data across systems without collisions, but they are larger than integers and randomly ordered, which can hurt index performance on very large tables. Many teams use UUIDs as public identifiers and integers internally.

Is anything sent to a server?

No. Generation happens entirely in your browser. The UUIDs you see are never transmitted, logged, or stored anywhere, so they are safe to use as secrets.