What is UUID (Universally Unique Identifier)?
Also known as: GUID, globally unique identifier.
Last updated: July 2026
- UUID (Universally Unique Identifier)
- A UUID (universally unique identifier), also called a GUID, is a 128-bit identifier written as 36 characters in the form 8-4-4-4-12, e.g. 550e8400-e29b-41d4-a716-446655440000. Version 4 UUIDs are generated from random numbers, making collisions so improbable that independent systems can create them without any coordination.
Generate random v4 UUIDs (GUIDs) in bulk and copy them with one click. Free, instant and fully in-browser using the secure crypto API.
Why they're unique
A version-4 UUID has 122 random bits (per RFC 9562, which supersedes RFC 4122). The number of possible values is so vast that generating billions per second for many years still gives a negligible chance of a collision — which is why UUIDs are safe to create on many machines at once.
When to use one
Use a UUID when you need a unique identifier without a central counter: distributed systems, offline-first apps, merge-friendly database keys, or public IDs you don't want users to guess or enumerate sequentially.
FAQ
Can two UUIDs be the same?
In theory yes, but for version 4 the probability is so small it's ignored in practice.
Is a GUID the same as a UUID?
Yes — GUID is Microsoft's name for the same 128-bit identifier.