UUID Generator

A UUID Generator creates Universally Unique Identifiers — 128-bit labels formatted as xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx (e.g., 550e8400-e29b-41d4-a716-446655440000) that are designed to be unique across all computers, all networks, and all time without requiring a central authority to coordinate assignments. UUIDs are a foundational primitive in distributed software systems.

What makes a UUID universally unique?

UUID v4 (random) is the most commonly used variant. It generates 122 bits of cryptographically random data, making the probability of two independently generated v4 UUIDs colliding astronomically small — approximately 1 in 5.3 × 10³¶. To put that in perspective: generating a billion UUIDs per second for 85 years would still have only a 50% chance of producing a collision.

UUID v1 incorporates the MAC address of the generating machine and the current timestamp, making the generated value traceable to a specific time and network interface. This provides monotonic ordering by generation time, which is useful for database insert ordering, but leaks machine information — a privacy consideration noted in RFC 4122.

GUID (Globally Unique Identifier) is Microsoft's term for UUID; the format and behaviour are identical. GUID is the standard terminology in .NET, SQL Server, and Windows development.

Where UUIDs are used

Primary keys in databases: Unlike auto-incrementing integers, UUID primary keys allow records to be created on multiple machines or by multiple services and merged into a single database without collision. This is essential for distributed systems, offline-first apps, and multi-region deployments.

API resource identifiers: REST API resources are often identified by UUIDs in the URL (/users/550e8400-e29b-41d4-a716-446655440000). Unlike sequential integers, UUIDs don't leak the total number of records or allow enumeration attacks.

Session tokens and correlation IDs: Each user session, request trace, or log correlation ID is assigned a UUID so events from distributed microservices can be traced back to a single request.

File names for uploaded content: Storing user-uploaded files with UUID names prevents filename collisions and doesn't expose original filenames to other users.

Testing and mocking: Generating realistic-looking IDs for test fixtures, seed data, or mock API responses without running an actual database.

The UtilsGo UUID Generator uses the browser's crypto.getRandomValues() API — the same cryptographically secure random number generator used for TLS and authentication — to generate v4 UUIDs. No UUIDs are logged or recorded.