Generate random UUIDs instantly
When two computers need to create identifiers without talking to each other, they need a way to guarantee those identifiers will not collide. That is exactly what a UUID provides. This free UUID generator creates random version 4 UUIDs (also called GUIDs) instantly in your browser. Generate a single identifier or a batch of up to 100, copy them individually or all at once, and switch between lowercase and uppercase output. It is fast, private and requires no sign-up.
What a UUID is
A UUID — Universally Unique Identifier — is a 128-bit value usually written as 32 hexadecimal digits split into five groups, like 3f2504e0-4f89-41d3-9a0c-0305e82c3301. Microsoft's equivalent term is GUID (Globally Unique Identifier), but they mean the same thing. The entire point of a UUID is that anyone, anywhere, can generate one at any time and be confident it will not clash with a UUID generated by someone else. That property — uniqueness without a central authority handing out numbers — is what makes them so valuable in distributed systems.
Why version 4 UUIDs are practically collision-proof
There are several UUID versions, but version 4 is the most common because it is generated purely from random numbers. Of its 128 bits, 122 are random, which yields roughly 5.3 x 10^36 possible values. To put that in perspective, you could generate a billion UUIDs every second for a hundred years and still have only an infinitesimal chance of ever seeing a duplicate. For any real application, you can treat version 4 UUIDs as guaranteed unique. The generator here uses your browser's cryptographically strong random source, so the values are both unique and unpredictable.
Anatomy of a UUID
A version 4 UUID follows the pattern xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx. The 4 in the third group marks the version, and the y at the start of the fourth group is always one of 8, 9, a or b, indicating the variant. Every other digit is random. Those two fixed positions are how software can recognise a well-formed version 4 UUID, while the randomness everywhere else is what makes collisions so astronomically unlikely.
Where UUIDs are used
UUIDs are everywhere in modern software. They serve as database primary keys, letting different services insert records without coordinating on the next available number. They act as correlation IDs in logs, so a single request can be traced across many microservices. They make excellent file names when you need to store uploads without collisions. They are used as idempotency keys so an API can safely ignore a duplicated request, and as opaque session or resource identifiers in URLs. Anywhere you need a unique handle that can be created offline and in parallel, a UUID fits.
How to use the generator
Enter how many UUIDs you need — anywhere from one to a hundred — and optionally switch to uppercase formatting to match your system's conventions. Click generate, then copy a single value with its button or grab the entire list at once. Because everything runs in your browser, you can produce identifiers for seeding a database, populating test data or scripting a quick task without ever hitting a server. It is a small utility that developers reach for constantly, and having a reliable, private generator a click away saves time on exactly the kind of routine work that would otherwise interrupt your flow.
UUIDs versus auto-incrementing IDs
A common design decision is whether to identify database records with UUIDs or with simple auto-incrementing numbers (1, 2, 3 and so on), and each has clear trade-offs. Auto-incrementing IDs are compact, human-friendly and naturally ordered, which makes them easy to read and efficient to index. But they must be generated by a single central authority — usually the database — so two systems cannot create records independently without risking a clash, and they leak information: an ID of 5,000 quietly tells a competitor roughly how many customers you have. UUIDs solve both problems. Because any machine can generate one offline with no coordination, they are ideal for distributed systems, offline-first apps and merging data from multiple sources. They also reveal nothing about volume or order. The cost is that they are longer, not human-memorable, and slightly less efficient to index. Many modern systems use UUIDs precisely because the ability to generate identifiers anywhere, at any time, without collisions outweighs the extra size. Knowing the trade-off helps you choose the right identifier for each part of your application.
Frequently asked questions
What is a UUID?
A UUID (Universally Unique Identifier), also called a GUID, is a 128-bit value written as 32 hexadecimal digits in five groups. It is designed to be unique without any central coordination.
What is a version 4 UUID?
A version 4 UUID is generated from random numbers. With 122 random bits, the chance of ever producing a duplicate is negligible for any practical purpose.
Are these UUIDs secure and random?
Yes. They use the browser's cryptographically strong random source, and generation happens locally, so no UUID is ever transmitted or logged.
What are UUIDs used for?
They are widely used as database primary keys, request and transaction IDs, file names, session tokens and any place needing a unique identifier that can be created independently.