HYLAS // UUIDGEN

// UUID VERSIONS

v1 — TIME-BASEDEncodes MAC address + timestamp. Sortable but leaks hardware info.

v2 — DCE SECURITYLike v1 with POSIX UID/GID. Rarely used.

v3 — MD5 HASHDeterministic from namespace + name. Same input = same UUID.

v4 — RANDOMCryptographically random. Most widely used. 122 bits of randomness.

v5 — SHA-1 HASHDeterministic from namespace + name. Prefer over v3.

v6 — REORDEREDv1 bits reordered for sortability. Proposed RFC.

v7 — UNIX TIMEMillisecond timestamp prefix + random. Sortable + DB-friendly.

// FORMAT GUIDE

UUIDxxxxxxxx-xxxx-Mxxx-Nxxx-xxxxxxxxxxxx (36 chars, 32 hex + 4 hyphens)

M (version)4th group, 1st char = version number (1-7)

N (variant)3rd group, 1st char = 8,9,a,b → RFC 4122

ULID26 Crockford Base32 chars. First 10 = timestamp, last 16 = random. Lexicographically sortable.

NanoIDURL-safe chars [A-Za-z0-9_-]. Default 21 chars. ~2.7× smaller than UUID for same collision resistance.

NIL UUID00000000-0000-0000-0000-000000000000. Used as null/default value.