generatorsname

UUID generator

Choose how many identifiers you need and generate them with the browser's crypto.randomUUID — 128-bit version 4 UUIDs, made and shown only in this tab.

Runs locally in your browser

How it works

A version 4 UUID is 128 bits written as 32 hexadecimal digits in five groups of 8-4-4-4-12. Of those 128 bits, 122 are random and 6 are fixed: the first character of the third group is always 4, marking version 4, and the first character of the fourth group is always one of 8, 9, a or b, marking the RFC 4122 variant. The browser's crypto.randomUUID sets those bits for you; where it is missing, the tool fills 16 bytes from crypto.getRandomValues and applies the same two masks by hand. The uppercase option only changes the letters — the value is the same identifier either way.

Worked example

Take 550e8400-e29b-41d4-a716-446655440000 and check it against the two rules. The third group is 41d4, which starts with 4, so the version is right. The fourth group is a716, which starts with a — in binary a is 1010, so the top two bits are 10, the RFC 4122 variant. Both rules hold, so it is a genuine version 4 UUID, and any v4 identifier you generate here will pass the same two checks.

Questions and answers

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