What is a UUID?

A UUID (Universally Unique Identifier) is a 128-bit identifier standardized by RFC 4122. It is represented as a 32-character hexadecimal string grouped by hyphens in the format: xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx

Version 4 UUIDs are generated using random (or pseudo-random) numbers. With 2¹²² possible values (~5.3 × 10³⁶), the probability of generating a duplicate UUID even across billions of generated identifiers is astronomically small — effectively impossible in practice.

UUID Versions Explained

v1 – Time-based. Generated from the current timestamp and the MAC address of the machine. Not recommended for privacy-sensitive use cases.
v3 – Namespace + MD5 hash. Deterministic — the same inputs always produce the same UUID. Used for consistent IDs from URLs or DNS names.
v4 – Random. The most common type. Generated from 122 random bits. No machine or time information is encoded. This tool generates v4 UUIDs.
v5 – Namespace + SHA-1 hash. Same as v3 but uses SHA-1 instead of MD5, providing better collision resistance.

Common Uses for UUIDs

Database primary keys – Globally unique across distributed systems without coordination between nodes.
Session and request IDs – Trace individual requests through complex microservice architectures.
Idempotency keys – Prevent duplicate operations in payment APIs and message queues.
File storage – Avoid naming conflicts when storing user-uploaded files in object storage (S3, GCS).
Feature flags – Identify users in A/B testing systems without exposing internal IDs.

Frequently Asked Questions

Is a UUID the same as a GUID?

Yes. GUID (Globally Unique Identifier) is Microsoft's term for the same standard. UUIDs and GUIDs are interchangeable and follow the same RFC 4122 specification.

Can two generated UUIDs ever be the same?

Theoretically yes, but practically impossible. With 2¹²² random values, generating a duplicate would require producing more IDs than there are atoms in the observable universe.

Should I use UUIDs as database primary keys?

UUIDs are excellent for distributed systems where you need IDs that are unique across multiple databases. The trade-off is slightly worse index performance compared to sequential integers. UUID v7 (ordered by time) is an emerging alternative that addresses this.

Are the generated UUIDs cryptographically random?

Yes. This tool uses crypto.randomUUID() or crypto.getRandomValues(), which uses the browser's CSPRNG — the same source used by password managers and security software.

UUID Generator