Question 1

What is a UUID v4?

Accepted Answer

UUID v4 (Universally Unique Identifier version 4) is a 128-bit identifier generated using random numbers. It's formatted as 36 characters in 8-4-4-4-12 groups (e.g., 550e8400-e29b-41d4-a716-446655440000).

Question 2

Are UUID v4 collisions possible?

Accepted Answer

The probability of two random UUIDs colliding is astronomically low — roughly 1 in 5.3×10³⁶. For practical purposes, UUID v4 can be considered unique.

Question 3

What is UUID v4 used for?

Accepted Answer

UUIDs are used as database primary keys, API resource identifiers, session tokens, transaction IDs, and anywhere unique identifiers are needed without a central authority.

Question 4

Is my data sent to a server?

Accepted Answer

No. UUID generation happens entirely in your browser using crypto.randomUUID() or fallback random generation.

Version	Method	Best For
v1	Timestamp + MAC address	Time-ordered IDs
v4	Random (cryptographic)	General purpose, uniqueness
v5	SHA-1 hash + namespace	Deterministic IDs from names
v7	Timestamp + random (RFC 9562)	Database-indexed IDs

UUID v4 Generator Online

UUID Version Comparison