UUIDTools.comAbout Version 4 UUIDs
A version 4 UUID is made almost entirely of random data: 122 of its 128 bits are random, and the other 6 bits record the version (4) and variant. It is the most widely used UUID and the right default when you just need a unique, unguessable identifier.
Our generator uses the operating system's cryptographically secure random number generator on the server. You can generate up to 1,000 at once, format them as GUIDs, and copy or download the result.
Structure
xxxxxxxx-xxxx-4xxx-Nxxx-xxxxxxxxxxxx (x = random, N = 8, 9, a or b)
When to use it
- General-purpose primary keys, request IDs, file names and API resource IDs.
- Anywhere identifiers must not reveal when or where they were created.
When to avoid it
- Large indexed database tables where insert locality matters: prefer v7, which is time-ordered.
Frequently asked questions
How likely is a UUID v4 collision?
With 122 random bits there are about 5.3 x 10^36 possible values. You would need to generate roughly 2.7 quintillion UUIDs to have a 50% chance of a single collision, so accidental duplicates are not a practical concern.
Is a v4 UUID safe to use as a secret?
It is unguessable when produced by a secure random source, but UUIDs are identifiers, not credentials. Use a purpose-built token for password resets and API keys.
Why use an online UUID generator?
Every language can generate UUIDs, but sometimes you just need one right now for a test fixture, a config file, a SQL insert or a bug report, without opening a REPL. UUIDTools gives you any RFC 9562 version in one click, in the exact format you need, and the same thing is available from the API for scripts.
Not sure which version to pick? Use v4 for plain random IDs and v7 for database keys. See UUID versions explained.