uuid generator.

UUID v1 uses timestamp + MAC address (traceable). v4 is random (most common). v7 is time-ordered random, ideal for database primary keys.

Use v4 for most applications. Use v7 for database primary keys (better index performance due to sequential ordering). Use v1 only if you need timestamp tracking.

v4 has 2^122 possible values — the chance of collision is astronomically low (1 in 5.3 quintillion). For practical purposes, they are unique.