A UUID is a 128-bit identifier designed to be unique without any central coordination. Any number of systems can generate them independently and never collide in practice, which is what makes them useful for distributed systems, database keys and correlation IDs.
How to use the UUID Generator
- Click Generate for a single UUID
- Use the bulk option to generate many at once
- Copy an individual value, or download the whole batch as a text file
Why collisions are not a practical concern
A version 4 UUID has 122 random bits, giving about 5.3 × 10³⁶ possible values. To reach a 50% chance of a single collision you would need to generate roughly 2.7 × 10¹⁸ of them — generating a billion per second, that is about 85 years.
The important caveat is that this only holds with a proper random source. This generator uses crypto.getRandomValues(), the browser's cryptographically secure RNG. UUIDs built from Math.random() — which some libraries still do — have far less real entropy and have caused collisions in production.
UUIDs as database keys
UUIDs let you generate an ID client-side before a row exists, which simplifies a great deal of distributed and offline-first work. The trade-offs are real though.
They are 16 bytes against 4 or 8 for an integer, which inflates every index that references them. More significantly, v4 UUIDs are random, so inserts land at random points in a B-tree index rather than appending at the end. On a large table that fragments the index and measurably hurts write throughput.
Where this matters, UUID v7 — which puts a timestamp in the high bits so values sort chronologically — gives you global uniqueness with sequential insert behaviour.
Frequently asked questions
Are these UUIDs cryptographically secure?
Yes. They use crypto.getRandomValues(), the browser's CSPRNG — the same source used for cryptographic key material, not Math.random().
What does the 4 in version 4 mean?
The generation method. v4 is random; v1 is based on timestamp and MAC address; v5 is a hash of a namespace and name. The version is encoded in the 13th hex digit, which is always 4 here.
Can two UUIDs ever be the same?
Theoretically yes, practically no — with 122 random bits you would need to generate about 2.7 quintillion before a 50% chance of one collision.
Should I use UUIDs as primary keys?
They are excellent for distributed or offline-capable systems where IDs must be created before reaching the database. On very large, write-heavy tables consider UUID v7, which sorts chronologically and avoids index fragmentation.
Are generated UUIDs stored anywhere?
No. Generation is entirely local and nothing is recorded or transmitted.