UUID Generator

What is a UUID?

A UUID (Universally Unique Identifier) is a 128-bit value defined by RFC 9562 (May 2024, replaces RFC 4122) — designed so any system can generate one without coordination, and the chance of collision is effectively zero. The standard format is 32 hexadecimal digits in five hyphen-separated groups: xxxxxxxx-xxxx-Mxxx-Nxxx-xxxxxxxxxxxx where M indicates the version (1, 4, 7, etc.) and N the variant (8, 9, a, or b for the standard variant).

How "unique" is it really?

UUID v4 uses 122 bits of cryptographically random data (6 bits are reserved for version and variant). The collision probability for v4 is ~1 in 2¹²² ≈ 5.3 × 10³⁶ — astronomically low. By the birthday paradox, you'd need to generate ~2.71 quintillion UUIDs before there's a 50% chance of even one collision. For all practical purposes: safe to assume uniqueness without checking.

Where UUIDs shine

Distributed systems, microservices, mobile apps generating local IDs before sync, log correlation across services (request-id headers), file uploads where you can't risk name collision. UUIDs let you generate IDs offline without needing a central database sequence — critical for multi-region deployments and event sourcing.