UUID Generator

Generate UUIDs (v1, v4, v5, v7) and ULIDs. Bulk mode, format options, and decoded metadata.

All UUIDs generated using crypto.getRandomValues() — nothing is sent to any server.

Version

Namespace:

Count

Format

UUIDs

Click Generate to create UUIDs

Frequently Asked Questions

Are the generated UUIDs stored on your servers?

No. UUIDs are generated entirely in your browser — v4 (random) uses window.crypto.getRandomValues for cryptographic randomness, and v7 uses the local system clock. No generated IDs are transmitted, stored, or logged anywhere.

What is the difference between UUID v4 and UUID v7?

UUID v4 is fully random (122 random bits) with no ordering guarantee — unpredictable but unsuitable for database sort keys. UUID v7 embeds a 48-bit Unix millisecond timestamp in its most significant bits, so v7 UUIDs sort lexicographically in creation order, dramatically improving database index performance in high-insert workloads.

When should I use ULID instead of UUID?

ULID (Universally Unique Lexicographically Sortable Identifier) is ideal when you need time-sortable IDs in a URL-safe, compact format. Unlike UUID v7, ULIDs use Crockford's Base32 encoding producing 26-character, case-insensitive, URL-safe strings. Use ULID for log correlation, event streams, and distributed systems where human-readable time ordering matters.

UUID Versions Compared

Version	Algorithm	Sortable?	Best for
`v1`	Timestamp + MAC address	Partially (time-based)	Distributed systems needing time ordering, logging
`v4`	Fully random	No	General purpose — the most common choice for IDs
`v5`	Namespace + name → SHA-1 hash	No	Deterministic IDs for the same input (e.g., URL → UUID)
`v7`	Unix ms timestamp + random suffix	Yes — lexicographically sortable	Database primary keys — monotonically increasing, no fragmentation

ULID vs UUID

A ULID (Universally Unique Lexicographically Sortable Identifier) encodes a 48-bit millisecond timestamp followed by 80 bits of randomness in Crockford Base32. ULIDs are 26 characters vs 36 for a UUID (or 32 without hyphens), URL-safe by default, and sort correctly as strings. They're an excellent choice for database primary keys when insertion order matters.

UUID v5 (Deterministic)

v5 produces the same UUID for the same namespace + name combination. This is useful when you need a stable UUID for a known entity — e.g., always mapping example.com in the DNS namespace to the same UUID. The standard namespaces are: DNS, URL, OID, and X.500. The output is a SHA-1 hash of the namespace bytes concatenated with the name bytes, then formatted as a UUID with version/variant bits set.

When to Use Which

Use v4 for most cases: session tokens, API keys, object IDs where you don't need order. Use v7 (or ULID) as database primary keys to avoid index fragmentation and enable time-range queries. Use v5 when you need reproducible IDs for the same logical entity. Use v1 only when you need to trace the generating machine (though be aware it leaks the MAC address).

Coming soon for logged-in users: Save generated UUID sets to your history and mark frequently used UUIDs as favorites for quick reference.