UUID Generator

What Is a UUID?

A UUID (Universally Unique Identifier) is a 128-bit identifier designed to be unique across all space and time without a central authority assigning them. UUID v4 — the most widely used version — is generated using random numbers. The probability of generating two identical UUIDs is so astronomically low (roughly 1 in 5.3 undecillion) that it is considered impossible in practice. UUIDs are used everywhere in software: as database primary keys, resource identifiers in REST APIs, file names, session tokens and tracking IDs.

UUID Format

A UUID looks like: 550e8400-e29b-41d4-a716-446655440000

It is always 32 hexadecimal digits split into five hyphen-separated groups in an 8-4-4-4-12 pattern. For UUID v4, the third group always starts with 4 (version marker) and the fourth group starts with 8, 9, a or b (variant marker).

When to Use UUIDs

• Database primary keys — avoids sequential integer IDs that expose your total record count and make enumeration attacks trivial.
• Distributed systems — each service generates unique IDs independently with no central coordination or risk of collision.
• REST API resource identifiers — /users/550e8400-... is safer and more opaque than /users/1.
• File and asset names — prevents naming collisions in shared storage buckets (S3, GCS).
• Idempotency keys — send a UUID with each API request so the server can detect and ignore duplicate submissions.

UUID v4 vs Sequential IDs