What is a UUID?

A UUID is a 128-bit identifier designed to be unique without coordinating with a central counter. UUID v4 fills its random fields with secure random bits and sets the version and variant bits required by the standard.

What is a ULID?

A ULID is a 26-character identifier containing a 48-bit millisecond timestamp followed by 80 random bits, encoded with a case-insensitive Crockford Base32 alphabet. Its timestamp prefix makes ordinary string sorting follow creation time.

UUID v4 vs ULID

Choose UUID v4

Use it for broad library, database, and API compatibility when creation order should not be visible in the identifier.

Choose ULID

Use it when compact, sortable identifiers are valuable and exposing an approximate creation time is acceptable.

Collisions and security

Random identifiers have an extremely large space, but they are identifiers—not authentication secrets. Do not treat a UUID or ULID as proof that a caller is authorized. ULIDs also expose their embedded creation time.

Frequently asked questions

How are UUIDs generated here?

The tool prefers crypto.randomUUID() and uses a standards-compliant crypto.getRandomValues() fallback where necessary.

What does the UUID inspector verify?

It checks canonical syntax and reports the encoded version and variant. It does not determine where an identifier came from.