UUID versions at a glance
| Version | Based on | Best for |
|---|---|---|
| v4 | Random (122 bits) | General-purpose unique IDs — the safe default |
| v7 | Unix timestamp + random | Database primary keys, time-sortable IDs |
| v1 | Timestamp + node | Legacy systems that expect Gregorian-time UUIDs |
| v5 | SHA-1 of namespace + name | Deterministic IDs — same input, same UUID |
| v3 | MD5 of namespace + name | Deterministic IDs where v3 is required for compatibility |
Frequently asked questions
What is a UUID?
A UUID (Universally Unique Identifier) is a 128-bit value used to uniquely identify information without a central authority. It is written as 36 characters: 32 hexadecimal digits in five groups separated by hyphens, e.g. 550e8400-e29b-41d4-a716-446655440000.
Which UUID version should I use?
Use v4 for a general-purpose random ID. Use v7 when you need IDs that sort by creation time — ideal for database primary keys. Use v5 (or v3) when the same input must always produce the same UUID.
Is this UUID generator safe to use?
Yes. Every UUID is generated locally in your browser using the cryptographically secure Web Crypto API. Nothing is sent to or stored on any server.
Are UUIDs really unique?
Collisions are astronomically unlikely. A v4 UUID has 122 random bits: you would need to generate about 2.7 quintillion UUIDs to reach a 50% chance of a single collision.
What is the difference between UUID and GUID?
They are the same 128-bit format. GUID (Globally Unique Identifier) is simply Microsoft's name for UUID.