UUID Generator

What is a UUID?

A UUID (Universally Unique Identifier) is a 128-bit identifier standardised by RFC 4122. It is formatted as 32 hexadecimal digits displayed in five groups separated by hyphens, following the pattern xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx. The "4" in the third group indicates version 4, meaning the UUID is generated from random or pseudo-random numbers. UUIDs are designed so that anyone can create one without a central authority and be virtually certain it will never collide with another UUID generated anywhere else.

How does this generator work?

This tool uses the Web Crypto API available in modern browsers. Where supported, it calls crypto.randomUUID() directly for maximum simplicity and performance. In older browsers that lack that method, it falls back to crypto.getRandomValues() to fill a byte array and manually assembles the UUID string with the correct version and variant bits. Either way, the randomness is cryptographically secure. Nothing leaves your browser - all generation happens client-side, so your UUIDs are never transmitted over the network or stored on any server.

Common use cases

Developers use UUIDs as primary keys in databases because they can be generated independently across distributed systems without coordination. They appear as transaction identifiers in payment processing, session tokens in web applications, correlation IDs in microservice architectures, and file names for uploaded content. UUIDs are also used in desktop software for component registration, in mobile apps for anonymous device identification, and in IoT systems where devices need unique identifiers without contacting a central server. Testers and QA engineers generate UUIDs to populate test data, while API designers use them as idempotency keys to prevent duplicate operations.

UUID v4 collision probability

A UUID v4 has 122 random bits, giving roughly 5.3 x 10^36 possible values. To have a 50% chance of a single collision, you would need to generate about 2.7 x 10^18 UUIDs - that is 2.7 quintillion. In practical terms, if you generated one billion UUIDs per second, it would take over 85 years to reach that threshold. For nearly all applications, the probability of a collision is effectively zero.