UUID Generator

A UUID is a 128-bit identifier written as 36 characters, designed so that anything can generate one at any time without coordinating with anything else and still not collide. That property is what makes them useful: you can create an ID on the client, in a worker, or across three services, and safely assume it is unique.

Version 4 is 122 random bits. It is the default choice, and the right one whenever the identifier must not reveal anything — no creation time, no ordering, no relationship to any other ID.

Version 7 puts a 48-bit millisecond timestamp at the front, followed by 74 random bits. Because the timestamp is the most significant part, sorting v7 UUIDs as strings sorts them by creation time.

That difference matters for databases. Random v4 keys scatter inserts across a B-tree index, fragmenting pages and hurting write throughput on large tables. v7 keys append in order, which behaves much more like an auto-incrementing integer while keeping the "generate anywhere" property. Use v7 for primary keys; use v4 when the identifier is public and should leak nothing.

The trade-off is exactly that leak: a v7 UUID tells anyone who holds it roughly when the record was created. This tool will show you — paste one into the inspector above.

1. Pick v4 or v7.
2. Choose how many you need — up to a thousand at a time.
3. Copy them all, or download them as a text file, one per line.
4. Use the inspector to validate a UUID and identify its version.

Every UUID here comes from crypto.getRandomValues(), the browser's cryptographically secure random number generator — not Math.random(), which is predictable and unsuitable for identifiers that must not be guessable. Generation happens entirely in this tab.

• Primary keys for distributed systems, where an auto-increment sequence is impractical.
• Correlation and trace IDs for following a request across services.
• Idempotency keys so a retried request is not processed twice.
• Filenames for uploads that must not collide.
• Seed data and fixtures during development.

• A UUID is unique, not secret. A v4 UUID is unguessable in practice, but treating identifiers as access control is still a mistake.
• A v7 UUID discloses its creation time to anyone who has it.
• Stored as text, a UUID is 36 bytes against 8 for a bigint. Most databases have a native UUID type that stores the underlying 16 bytes — use it.
• Generating a thousand at once briefly makes a large page of text; the browser handles it, but pasting it somewhere may not be quick.