Can two UUID v4 values ever collide?

It is theoretically possible but astronomically unlikely. With 122 random bits, you would need to generate an impractical number of UUIDs before a collision became plausible.

Is a GUID the same as a UUID?

Yes. GUID (Globally Unique Identifier) is Microsoft's name for the same 128-bit identifier concept.

Does this send my data anywhere?

No. Utilumo's developer tools parse and transform input inside the browser tab. Nothing is uploaded, stored, or logged.

Explainer1 min readUpdated June 25, 2026

What is a UUID?

Short answer

A UUID (Universally Unique Identifier) is a 128-bit value used as an identifier that does not need a central server to stay unique. The most common form, UUID v4, is almost entirely random, so two generated values practically never collide.

What a UUID looks like

A UUID is written as 32 hexadecimal digits in five groups separated by hyphens, in the pattern 8-4-4-12.

f47ac10b-58cc-4372-a567-0e02b2c3d479

A UUID v4 value

Why it stays unique

UUID v4 fills almost all of its 128 bits with random data (122 bits after the version and variant markers). The space is so large that generating values randomly will, in practice, never produce a duplicate, even across many independent machines that never talk to each other.

Versions matterv4 is random. v7 is newer and time-ordered, which makes it friendlier for database indexes because values sort roughly by creation time. Both are defined in RFC 9562.

Try it: UUID GeneratorGenerate UUID v4 values locally using the browser crypto API.Open tool

When to use a UUID

Identifiers you must create on the client before talking to a server
Keys that must be unique across multiple databases or services
Public ids where a guessable, sequential number would leak information

When not to use one

Random UUIDs are larger than integers and do not sort by creation order, which can hurt database index performance. If you need ordered keys, consider UUID v7 or a database sequence instead.