What is a UUID?
A UUID (Universally Unique Identifier) is a 128-bit label used to uniquely identify objects in computer systems. The probability of generating a duplicate UUID v4 is astronomically low — roughly 1 in 5.3 × 10³⁶.
UUID v4 Structure
Format: xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx
- 32 hexadecimal digits in 5 groups separated by hyphens
- The 4 at position 13 indicates version 4 (random)
- The y at position 17 is one of
8, 9, a, b (variant bits)
- All remaining bits are randomly generated
UUID Versions
| Version | Method | Use Case |
|---|
| v1 | Time + MAC address | Sortable IDs (exposes network info) |
| v3 | MD5 hash of namespace + name | Deterministic, reproducible IDs |
| v4 | Random (CSPRNG) | Most common — general purpose unique IDs |
| v5 | SHA-1 hash of namespace + name | Better deterministic than v3 |
| v7 | Unix timestamp + random | Sortable + random (modern standard) |
Frequently Asked Questions
Are these UUIDs truly unique?
Yes. This tool uses crypto.randomUUID() or crypto.getRandomValues() — the browser's cryptographically secure random number generator. The probability of two v4 UUIDs colliding is approximately 1 in 5.3 undecillion (10³⁶). For all practical purposes, they are unique.
Can I use these UUIDs as database primary keys?
Absolutely. UUID v4 is widely used as a primary key in databases like PostgreSQL (uuid type), MySQL, and MongoDB. The main tradeoff vs sequential integer IDs is slightly larger storage and worse index locality — mitigated by UUID v7 if ordering matters.
Are UUIDs generated here stored anywhere?
No. Generation happens 100% in your browser using the Web Crypto API. Nothing is sent to any server.