UUID Generator

What is a UUID?

A UUID (Universally Unique Identifier), also known as a GUID (Globally Unique Identifier), is a 128-bit value used to uniquely identify information without a central authority. It is represented as 32 hexadecimal digits displayed in five groups separated by hyphens — for example: 550e8400-e29b-41d4-a716-446655440000.

UUIDs are used everywhere in software: database primary keys, session tokens, file names, distributed system node IDs, and more. The format guarantees uniqueness across time and space without coordination between systems — making it safe to generate them independently on any machine.

UUID versions

• v1 — Time + node — generated from the current timestamp and a node identifier (MAC address or random). Unique across time but encodes when and where it was created.
• v2 — DCE Security — a variant of v1 that encodes a POSIX UID/GID and domain. Rarely used in practice.
• v3 — Name-based (MD5) — deterministic: given the same namespace UUID and name, it always produces the same UUID. Uses MD5 hashing.
• v4 — Random — generated from 122 bits of random data. The most commonly used version — no time or name information encoded.
• v5 — Name-based (SHA-1) — like v3 but uses SHA-1 instead of MD5. Preferred over v3 when you need deterministic, name-based UUIDs.
• v6 — Reordered time — a reordering of v1 fields that makes the UUID sortable by creation time. Designed for database use cases.
• v7 — Unix timestamp — uses a millisecond-precision Unix timestamp in the most significant bits, making it naturally sortable. The recommended choice for new database primary keys.
• v8 — Custom — vendor or application-specific format. The layout of bits is not defined by the standard — the version and variant bits are the only fixed fields.