UUID Generator
Generate random UUIDs (Universally Unique Identifiers) v4 instantly. Generate single or bulk UUIDs for development.
About this calculator
Generate random version-4 UUIDs, one at a time or in bulk, and copy them all. A UUID is a 128-bit identifier written as 32 hex digits in the form 8-4-4-4-12.
They are used as database keys, request IDs and file names where uniqueness matters without a central counter.
How to use it
- Enter How many UUIDs.
- Press Generate UUID(s).
- Press Copy All.
Version 4 UUIDs
A v4 UUID has 122 random bits. The 13th hex digit is always 4 (the version) and the 17th is one of 8, 9, a, b (the variant). Example: f47ac10b-58cc-4372-a567-0e02b2c3d479. The chance of two random v4 UUIDs colliding is negligible: you would need to generate about 2.7 quintillion to reach a 50% chance.
Worked example
Format
| Pattern | xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx |
| y | 8, 9, a or b |
Tips and common mistakes
- UUIDs are not secrets; do not use them as passwords.
- Store as binary (16 bytes) in databases for speed.
- Random UUIDs can hurt index locality; consider time-ordered UUIDs (v7) for primary keys.
- Lower-case hex is the common convention.
- Don't depend on UUID ordering.
Frequently asked questions
What is a UUID?
A 128-bit universally unique identifier.
Are UUIDs really unique?
Collisions are astronomically unlikely.
What is the difference between UUID and GUID?
GUID is Microsoft's name for the same thing.
What does version 4 mean?
Randomly generated.
How long is a UUID?
36 characters with hyphens.
Can I use UUIDs as secure tokens?
Prefer a purpose-built random token.