UUID Generator

What is a UUID?

A UUID (Universally Unique Identifier) is a 128-bit identifier standardized by RFC 4122. It is written as 32 hexadecimal digits arranged in five groups separated by hyphens: xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx.

UUIDs are designed to be unique across space and time without requiring a central authority. They're generated independently on any machine, making them ideal for distributed systems, microservices, and client-side ID generation before a server round-trip.

UUID v4 vs UUID v7

Collision probability

UUID v4 has 122 random bits. The probability of generating two identical UUIDs is astronomically small. To have a 50% chance of a single collision, you would need to generate approximately 2.7 × 10¹⁸ UUIDs — roughly one UUID per second for 86 billion years.

For practical purposes, UUIDs are collision-free. You do not need a uniqueness check before inserting one into a database.

Storage and performance tips

• Store UUIDs as BINARY(16) or a native UUID type (PostgreSQL uuid, MySQL 8 UUID) rather than VARCHAR(36) to save space and speed up indexes.
• For MySQL/InnoDB with v4 UUIDs, consider v7 instead — sequential IDs insert at the end of the B-tree rather than fragmenting it.
• Never rely on UUID sort order to mean insertion order unless using v7 or v1 (time-based).

Common uses

• Database primary keys — generate the ID on the client before inserting a row, enabling optimistic UI updates
• Distributed systems — generate IDs across multiple services without coordination
• File names — name uploaded files with UUIDs to avoid collisions and prevent path guessing
• Feature flags and A/B testing — assign stable random IDs to experiment groups
• Testing fixtures — generate unique test IDs in bulk without worrying about conflicts

Edge cases and limits

• Browser support — crypto.randomUUID() requires a secure context (HTTPS or localhost). All modern browsers support it.
• Quantity limit — generation is capped at 100 per click to keep the UI responsive.
• Uppercase vs lowercase — both are valid representations of the same UUID. Use the toggle to match your codebase's convention.

FAQ