UUID / GUID Generator
Generate UUIDs in v1, v4, or v5 — bulk, formatted, with optional prefix/suffix.
Version Reference
v4 — Random
Version 4 UUIDs are generated entirely from random (or pseudo-random) bytes. 122 of the 128 bits are random; the remaining 6 bits encode the version (4) and the variant. Because they carry no structured information, v4 UUIDs are the simplest choice. Use v4 as the default for database primary keys, session tokens, and any context where uniqueness is required but time ordering is not.
Wikipedia — UUID Version 4 (random)
v1 — Time-based
Version 1 UUIDs embed a 60-bit timestamp (100-nanosecond intervals since 15 October 1582), a 14-bit clock sequence, and a 48-bit node identifier (historically the MAC address of the generating machine). v1 UUIDs sort chronologically when compared lexicographically. The trade-off is privacy: a v1 UUID leaks the machine's MAC address and the exact creation time.
Wikipedia — UUID Version 1 (time-based)
v5 — Namespace + Name (SHA-1)
Version 5 UUIDs are deterministic: given the same namespace UUID and the same name string, the output is always identical. The algorithm hashes them with SHA-1 and folds the result into 128 bits. This makes v5 ideal for generating stable, reproducible identifiers. v3 uses MD5 instead; v5 is preferred because SHA-1 produces fewer collisions.