What is the difference between UUID v1, v4, and v5?

UUID v1 uses the current timestamp and MAC address, making it time-sortable but potentially exposing hardware info. UUID v4 is fully random (122 random bits) and the most popular for general use. UUID v5 is deterministic — it always produces the same UUID for the same namespace + name input using SHA-1 hashing, ideal for reproducible identifiers.

Are the generated UUIDs truly unique?

UUID v4 has 2¹²² possible values, making collisions astronomically unlikely. For practical purposes, yes — these UUIDs are unique. UUID v5 outputs are deterministic, so the same inputs always produce the same UUID.

When should I use UUID v5 instead of v4?

Use UUID v5 when you need the same UUID for the same input every time — for example, a consistent identifier for a user based on their email. Use UUID v4 when you need a random, unique ID with no reproducibility requirement.

Can I use these UUIDs in my database?

Yes! UUIDs are widely used as primary keys in databases. PostgreSQL, MySQL, SQL Server, and MongoDB all natively support UUID types. Using UUIDs as keys avoids ID conflicts in distributed systems and makes merging data from multiple sources much easier.

UUID Generator — Generate v1, v4, v5 UUIDs Online Free

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UUID Generator

UUID Version

How many UUIDs?

Format

Frequently Asked Questions

A UUID (Universally Unique Identifier) is a 128-bit label used to uniquely identify information in computer systems. It's represented as 32 hexadecimal digits in 5 groups separated by hyphens, e.g. 550e8400-e29b-41d4-a716-446655440000. UUIDs are designed to be globally unique without requiring a central registration authority.

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