How to use the UUID Generator
Set how many UUIDs you need and the output format, then generate and copy. Each one is built from cryptographically secure random bytes where your browser supports it.
What a UUID looks like
A UUID is 128 bits written as 32 hex digits in five groups, such as 3f1c9a2e-7b4d-4e8a-9c1f-2a6b5d8e0f47. In version 4, 122 of those bits are random. The 4 at the start of the third group marks the version, and the first digit of the fourth group shows the variant.
Can two UUIDs clash?
In practice, no. With 122 random bits, you would need to create billions of UUIDs every second for many decades before a duplicate became likely. That is why systems can create IDs on different machines without checking with each other. They are identifiers, though, not secrets, so do not use them as passwords.
UUID versions explained
UUIDs, universally unique identifiers, were first standardised in RFC 4122, which RFC 9562 replaced in 2024. Version 1 mixes a timestamp with the MAC address of the machine, which can leak information. Version 4, made here, is built from random numbers. Version 7 starts with a timestamp, so time ordered IDs sort in the order they were created. GUID, globally unique identifier, is the name Microsoft uses for the same thing.
Using UUIDs as primary keys
UUIDs work well as primary keys in distributed systems, because each server can create IDs without asking a central database. The trade-off is size: a UUID takes 16 bytes as binary and 36 characters as text, and random version 4 values scatter new rows across a database index. For very large tables, many teams store them in a binary column or use version 7 instead.
How it works
Cryptographically secure random bytes when supported
Examples
- Worked example
A UUID v4 has the form xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx.
Limitations and assumptions
UUIDs are identifiers, not passwords or authentication secrets.
Frequently asked questions
What is a version 4 UUID?
A UUID built mostly from random bits, as opposed to versions based on time or names.
Are these UUIDs unique?
For all practical purposes, yes. The chance of a repeat is vanishingly small.
Is GUID the same as UUID?
Yes. GUID is the name Microsoft uses for the same format.