Unique identifier
Version 4 UUIDs, generated on your device and never sent anywhere.
Runs locally in your browser. Nothing you generate is ever sent to a server.
Press "Generate" for a UUID.
Format
Version 4, 122 random bits each
Press Generate for a version 4 UUID, made on your own device from your browser's cryptographic random source. Nothing is sent to a server, which matters when the identifier is going into your own system.
UUID version 4 is the random one. Of its 128 bits, six are fixed to record the version and variant, and the remaining 122 are random. That is why the third group always starts with a 4 and the fourth group always starts with 8, 9, a or b. If a generator produces UUIDs without those markers, it is not producing valid version 4 UUIDs, whatever it says.
With 122 random bits there are roughly 5.3 undecillion possible values. To reach a one in a billion chance of a single collision you would need to generate about 103 trillion UUIDs. In any real system the risk of a collision is far smaller than the risk of the disk failing, which is why UUIDs can be created independently on many machines without coordination.
Lowercase with dashes is the canonical form and the one to use unless something specific requires otherwise. Uppercase appears in some Microsoft tooling, the plain 32-character form suits places where dashes are inconvenient, and the braced form turns up in Windows registry entries and older APIs.
Sixteen random bytes are drawn from your browser's cryptographic random source, then the version and variant bits are set as the specification requires and the result is formatted. Values falling outside a clean multiple of the byte range are discarded and redrawn, so every possible UUID is equally likely.
A 128-bit identifier written as 36 characters, designed so that anyone can generate one at any time without checking with anyone else and still not collide with an existing one.
Version 4, the random one. The version digit is always 4 and the variant digit is always 8, 9, a or b, exactly as the specification requires.
In theory yes, in practice no. There are about 5.3 times 10 to the 36 possible version 4 UUIDs, so a collision is far less likely than the hardware failing while you generate them.
Yes. Set the count up to 500 and press once, then Copy All to paste the whole list into a fixture file or a database seed.
Yes. The format buttons switch between lowercase, uppercase, no dashes and braces, which covers the forms different systems expect.
Yes. The random bytes come from your browser's cryptographic random source, and nothing is sent anywhere - the UUIDs are made on your own device.