UUID Generator

A UUID is a 128-bit identifier represented as 32 hexadecimal digits in the familiar 8-4-4-4-12 layout. Version 4 fills the random field with cryptographically secure random bytes and is the established choice when identifiers should reveal no creation order. Version 7 places a Unix-millisecond timestamp at the front and random data after it. The resulting values sort roughly by creation time, which can improve database index locality while remaining globally unique without a central counter.

UUID generation does not query a registry. Uniqueness comes from an enormous value space: a conforming v4 UUID has 122 random bits after version and variant markers, making accidental collision extraordinarily unlikely for ordinary application volumes. Version 7 combines time with random bits. Neither format is a secret, an authentication token, or proof of identity. Treat UUIDs as public identifiers unless a separate authorization layer protects the referenced object.

Choose v4 for opaque record IDs or request correlation where ordering is irrelevant. Choose v7 for new database primary keys when time ordering and index insertion behavior matter, after confirming your language and database libraries support it. Generate a small batch here for fixtures, API examples, migration scripts, or manual testing. Production code should generate identifiers inside the application at the moment records are created rather than depending on values copied from a webpage.

The canonical textual form uses lowercase hexadecimal characters and hyphens. The first hexadecimal digit of the third group identifies the version: 4 for UUID v4 and 7 for UUID v7. The first digit of the fourth group encodes the RFC variant and is normally 8, 9, a, or b. A string matching the shape is not necessarily trustworthy; validation should check both syntax and the accepted version, and authorization must still be enforced separately.

• Are the generated UUIDs sent to TmpKit? — No. They are produced locally and are not recorded by the site.
• Can I use a UUID as a password or API key? — No. Identifiers are not credentials, and v7 intentionally exposes approximate creation time.
• Which version should I choose? — Use v4 for opaque randomness and v7 when time-sortable database identifiers are beneficial.
• Can a collision happen? — It is mathematically possible but extraordinarily unlikely with correct generation; applications should still enforce a unique constraint.