UUID Generator

A UUID (Universally Unique Identifier) is a 128-bit identifier that's unique in practice without a central registry: two independent servers can generate one at the same moment and almost never collide. The versions differ in how they're generated.

Which version to pick

• v4 — fully random, the most common choice for database record IDs, session keys, and similar cases.
• v1 and v6 — based on creation time; v6 carries the same content as v1 but with the fields reordered so it sorts naturally — handy as a primary key.
• v3 and v5 — deterministic, derived from a namespace and a name (v3 uses MD5, v5 uses SHA-1) — the same input always produces the same UUID.
• v7 — the newest standard: a millisecond Unix timestamp plus a random part, sortable by time like v1/v6, but without a MAC address.

Common uses

• Primary keys in databases where auto-increment doesn't fit (distributed systems, offline-first apps).
• Session IDs, request IDs for tracing, temporary file names.
• Deterministic IDs (v5) for objects that need the same identifier across different systems given the same name.

Things to keep in mind

UUID v1 and v6 embed the generating device's MAC address — avoid them if that's an unwanted disclosure.

The format is 32 hexadecimal characters grouped with hyphens as 8-4-4-4-12 (e.g. 550e8400-e29b-41d4-a716-446655440000).