About UUID v4
A UUID (Universally Unique Identifier) v4 packs 122 bits of randomness into the familiar 36-character format xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx — the 4 marks the version, and y encodes variant bits (8, 9, a or b). This tool uses crypto.getRandomValues(), the browser's cryptographically secure RNG — the same source used by password managers, never Math.random().
Collision odds are astronomically small: you'd need ~2.7 quintillion UUIDs for a 50% chance of a single duplicate. That's why UUIDs are the default for database keys, request IDs and distributed systems. Need random numbers instead? Try the Random Number Generator.