What is a UUID?
A UUID (Universally Unique Identifier) is a 128-bit value used to label information without a central authority to hand out IDs. Written as 32 hexadecimal digits in the familiar 8-4-4-4-12 format, a UUID can be generated independently on any machine with a negligible chance of ever colliding with another. That property — globally unique, no coordination required — is why UUIDs are the default identifier for database rows, API resources, event streams, and distributed systems. This tool generates them to RFC 9562, the 2024 standard that supersedes RFC 4122.
UUID v4 vs v7
The practical choice in 2026 is between UUID v4 and UUID v7, and it comes down to one thing: whether the ID should be sortable by creation time. UUID v4 is 122 bits of cryptographically random data — collision-safe and revealing nothing about when it was made. UUID v7 replaces the leading bits with a 48-bit Unix-millisecond timestamp, so IDs generated later sort after earlier ones while keeping the same uniqueness guarantees.
That difference matters most in a database. A v4 primary key lands at a random position in a B-tree on every insert, causing page splits and cache thrashing as the table grows. A v7 primary key inserts in roughly increasing order, so consecutive rows hit the same hot index page — B-tree behavior close to an auto-increment integer, but without a central sequence. PostgreSQL 18 ships a native uuidv7(), and because most ORMs treat UUIDs as opaque 128-bit values, moving from v4 to v7 is usually a one-line change.
Working through the choice properly? Compare UUID v4 and UUID v7 side by side. If you want the format itself explained first, read what a UUID is. Or jump straight to the dedicated UUID v7 generator or UUID v4 generator.
When to use which
| Use case | Recommended | Why |
|---|---|---|
| Database primary key | v7 | Time-ordered inserts keep B-tree indexes healthy |
| Session tokens, share links, reset URLs | v4 | Creation time must not leak; pure randomness |
| Event / log correlation IDs | v7 | Natural time sort aids debugging |
| Public-facing opaque IDs | v4 | No ordering information exposed |
| Offline / distributed generation | either | Both need no central coordinator |
How this tool works
Every UUID is generated entirely in your browser and never sent to our
server. The randomness comes from the Web Crypto API
(crypto.randomUUID() for v4, crypto.getRandomValues()
for v7) — never Math.random() — so the values are
cryptographically unique. The generated ID exists only on your screen and in
your clipboard: it is never transmitted, stored, or logged.
The site itself loads Google Tag Manager to count anonymous page and feature usage, which sets cookies. That measurement never includes the UUIDs you generate.
Frequently asked questions
What is a UUID?
A UUID (Universally Unique Identifier) is a 128-bit identifier used to label information in computer systems without a central authority. Written as 32 hexadecimal digits in 8-4-4-4-12 format, it can be generated on any machine independently with a negligible chance of collision.
What does UUID stand for?
UUID stands for Universally Unique Identifier — a 128-bit number defined by RFC 9562 used to uniquely identify information across systems without requiring coordination.
What is a UUID used for?
UUIDs are used as database primary keys, distributed system identifiers, idempotency keys for API requests, event and trace IDs, and offline record creation — any situation where unique IDs must be generated without a central authority.
Is a UUID guaranteed to be unique?
Not mathematically guaranteed, but the collision probability is so small it's treated as unique in practice. You'd need to generate billions of v4 UUIDs before a collision became likely.
What's the difference between a UUID and a GUID?
None, in practice. GUID is Microsoft's name for the same 128-bit standard; the terms are interchangeable.
Should I use v4 or v7?
Use v7 for database primary keys (time-sortable, index-friendly) and v4 for anything where creation order could leak information, like tokens or share links.
Does this tool store or log my UUIDs?
No. Generation happens in your browser and the value never reaches our server. The UUID itself is never transmitted or recorded.
Can I generate UUIDs offline?
Yes. Once the page has loaded, generation is fully client-side and works with no network connection.