UUID Generator

Generate one or many random version-4 UUIDs (also called GUIDs) for database keys, identifiers and test data. They're created with a secure random source in your browser and can be copied with one click.

Choose how many and press Generate UUIDs.

What a UUID is

A UUID (Universally Unique Identifier), also called a GUID, is a 128-bit value written as 32 hexadecimal digits in five dash-separated groups: 8-4-4-12. Version 4 UUIDs are almost entirely random — only a few bits are fixed to mark the version and variant:

xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx

The 4 marks version 4, and y is one of 8, 9, A or B (the variant). The other 122 bits come from a secure random source, giving an enormous space of possible values.

Worked example

Reading a generated UUID like 3f2504e0-4f89-41d3-9a0c-0305e82c3301:

Version digit: the 13th hex digit is 4 → version 4 (random).
Variant digit: the 17th is 9 (8/9/a/b) → RFC 4122 variant.
Rest: 122 random bits — practically guaranteed unique.

Are collisions possible?

In theory, yes — but the odds are astronomically small. With 122 random bits there are about 5 × 10³⁶ possible v4 UUIDs. You'd need to generate billions per second for many years before the chance of any two matching became meaningful. For database keys, file names, session IDs and test data, v4 UUIDs are treated as effectively unique without coordination between systems.

Tip: need a short random token or code instead of a full UUID? Try the password generator or random number generator.

Frequently asked questions

What's the difference between a UUID and a GUID?

They're the same thing. UUID is the term used by the RFC standard; GUID is Microsoft's name for the identical 128-bit identifier. This tool generates version-4 (random) UUIDs that work as GUIDs.

Are these UUIDs really unique?

Effectively, yes. Version-4 UUIDs use 122 random bits, giving over 5×10³⁶ possibilities, so the chance of a collision is negligible for any realistic number of identifiers.

Can I generate many at once?

Yes. Set the count up to 500 and they're all generated instantly in your browser. Use Copy all to grab the whole list.

Is the randomness secure?

Yes. The UUIDs use the browser's cryptographically secure random generator (crypto.getRandomValues or crypto.randomUUID), not the weaker Math.random.

MB
Mustafa Bilgic · Editor, Calcool
UUIDs follow RFC 4122 version 4 and use the Web Crypto API for randomness. See the MDN randomUUID reference. Everything runs in your browser — nothing you enter is uploaded, logged or stored.

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