UUID Generator
Generate random, deterministic, and time-ordered UUIDs.
6ba7b810-9dad-11d1-80b4-00c04fd430c8
Hashing…
v4 uses crypto.randomUUID() — cryptographically random, 122 bits
of entropy. The probability of a collision across 1 billion UUIDs is about 1 in 1018.
v5 generates a deterministic UUID from a namespace and a name using a SHA-1 hash. The same inputs always produce the same UUID. Useful for stable IDs derived from natural keys — for example, a consistent UUID for a domain name or a database row identified by a natural key.
v7 embeds a 48-bit Unix millisecond timestamp in the first 6 bytes, followed by random bits. Because the timestamp comes first, v7 UUIDs sort lexicographically in generation order — making them well-suited as primary keys in databases where UUID ordering matters for index performance.
Base64 encoding represents the 16 raw UUID bytes as a 24-character string (22 characters in base64url without padding). Useful when you need a compact, URL-safe identifier.
What is a UUID?
A UUID (Universally Unique Identifier) is a 128-bit identifier formatted as 8-4-4-4-12 hexadecimal characters, e.g. 550e8400-e29b-41d4-a716-446655440000. They are designed to be globally unique without requiring a central registry.
What is the difference between UUID v4, v5, and v7?
v4 is completely random (122 bits of entropy). v5 is deterministic — the same namespace + name always produces the same UUID, using SHA-1. v7 encodes a millisecond timestamp in the first 48 bits so UUIDs sort in generation order — ideal for database primary keys.
What are the chances of a UUID collision?
Extremely small for v4. With 1 billion UUIDs, the probability of any collision is about 1 in 10^18. Generating a duplicate UUID in practice is essentially impossible.
Why use UUID v7 instead of v4 for database primary keys?
v4 UUIDs are random, causing random writes across a B-tree index — expensive for inserts at scale. v7 UUIDs are time-ordered, so new rows insert at the end of the index like an auto-incrementing integer, preserving locality and insert performance.
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Updated August 18, 2026