UUID & ULID Generator
Generate cryptographically random UUID v4, time-based UUID v1, and ULID values. Bulk generation up to 100 at once.
Generate Unique Identifiers
UUID Validator
UUID Versions Explained
- UUID v4 (Random): 122 random bits. Best for most use cases — extremely low collision probability (1 in 5.3×10^36). Use for session IDs, database primary keys, API keys.
- UUID v1 (Time-based): Encodes the current timestamp and MAC address. Sortable by creation time. Useful for distributed systems needing time-ordered IDs.
- UUID v3 & v5: Deterministic — same input always gives same UUID. v3 uses MD5, v5 uses SHA-1. Good for content-addressable IDs.
What is ULID?
ULID (Universally Unique Lexicographically Sortable Identifier) is a 128-bit identifier that is time-sortable and URL-safe. Format: 01ARZ3NDEKTSV4RRFFQ69G5FAV. Advantages over UUID: lexicographically sortable, URL-safe, readable, compatible with UUID-sized storage.
When to Use Each
- Database primary keys: UUID v4 or ULID (ULID is better for index performance)
- Session tokens / API keys: UUID v4 (pure random, unpredictable)
- Distributed event IDs: ULID or UUID v1 (time-ordered)
- Deterministic IDs: UUID v5 (hash-based)
- Short IDs in URLs: NanoID (shorter, URL-safe)