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UUID v4 generator

The UUID v4 generator produces random identifiers from the browser's cryptographic random number generator, in the familiar 8-4-4-4-12 layout of lowercase hex: 36 characters with a fixed version-4 digit. Developers use them for database primary keys, cache keys, idempotency headers and object names in test fixtures. A UUID is drawn when the tool opens; set "Count" for up to 100 at once, one per line, and tick "Uppercase" or "No hyphens" for the spellings some systems expect.

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How to use UUID v4 Generator

  1. Open UUID v4 Generator in the Toolbox101 app; a UUID is already in the Output box.
  2. Set Count if you need several (1 to 100), and tick Uppercase or No hyphens for the format you need.
  3. Click Generate New to draw again.
  4. Click Copy, then paste the UUIDs into your code, database or test fixture.

Worked example

UUID v4 Generator gives a different result every time, so yours will differ. This is one run:

Output

c1ca0971-749f-4368-aa53-172b6f59563d

Frequently asked questions

What is the difference between UUID v4 and UUID v1?

A v4 UUID is made of 122 random bits, so two values carry no relationship to each other or to the moment they were created. A v1 UUID encodes its creation time, clock sequence and node in the value, which makes v1 values roughly sortable but also reveals when they were made. The UUID v1 generator is the other half of this pair.

Can two UUID v4 values ever collide?

Theoretically yes, practically no. With 122 random bits you would need to generate about 2^61 values for a 50 percent chance of any duplicate, and the bits come from a cryptographically secure source. A collision between two of these values is not a realistic failure mode.

What format is a UUID v4?

Thirty-six characters in five hyphen-separated groups of 8-4-4-4-12 lowercase hexadecimal digits. The first digit of the third group is always 4, marking version 4, and the first digit of the fourth group is 8, 9, a or b, marking the RFC 4122 variant. Uppercase and No hyphens give the other two common spellings of the same value.

Use UUID v4 Generator now

Open UUID v4 Generator in the app

Runs in your browser. Nothing you type is uploaded.