UUID vs ULID — When to Use Which?
UUID (RFC 4122) and ULID (Universally Unique Lexicographically Sortable Identifier) are both 128-bit unique IDs. UUID is the standard 8-4-4-4-12 hex format; ULID is 26 characters, Crockford base32-encoded, with the first 48 bits as a millisecond timestamp and the rest random.
Format and Length
UUID: 36 characters with hyphens (e.g. 550e8400-e29b-41d4-a716-446655440000). ULID: 26 characters, no hyphens (e.g. 01ARZ3NDEKTSV4RRFFQ69G5FAV). ULID is shorter and URL-friendly; UUID is widely recognized and has native support in many databases and languages.
Sortability
Standard UUID v4 is random, so not sortable. UUID v7 is time-ordered like ULID. ULID is always lexicographically sortable by time. If you need sortability and prefer a compact string, ULID is a good fit; if you need RFC compliance and broad tooling, use UUID (v4 or v7).
When to Use Which
- UUID v4: Maximum compatibility, no ordering; default for APIs and many DBs.
- UUID v7: RFC-style ID with time ordering; good when you want standard format and sortability.
- ULID: Shorter, sortable, case-insensitive encoding; good for URLs, logs, and systems that don't require UUID format.
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