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UUID Validator

Free UUID validator. Check whether a UUID is well-formed, extract its version (1-8) and variant (RFC 4122, NCS, Microsoft), and normalize to the canonical lowercase hyphenated form. Runs in your browser.

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UUID

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Enter a UUID to validate it.

Deep dive guides

A LITTLE CONTEXT · 4 MIN READWhat a UUID's Bits Say About Where It Came From

All 4 related guides

How UUIDs Work — How 128-bit identifiers stay unique with zero coordination: versions 1/4/7, the 122-bit collision math, and the nil and max special values.
How Unix File Permissions Work — Three roles, nine bits, one octal digit each: what rwxr-xr-x and 755 really mean, plus setuid, setgid and the sticky bit.
How Semantic Versioning Works — MAJOR.MINOR.PATCH as a promise: what each bump means, how prerelease precedence works, and why 1.0.0 is where the contract begins.
What a UUID's Bits Say About Where It Came From — A UUID describes itself: the version nibble, the variant bits, the nil and max sentinels — and what validation proves (shape, not uniqueness).

How uuid validator works

A UUID (Universally Unique Identifier), also called a GUID, is a 128-bit identifier usually written as eight groups of hex digits separated by hyphens: 8-4-4-4-12 (36 characters total). This validator checks that your string matches that shape after accepting hyphenated, compact (32 hex), urn:uuid:, and braced {…} input forms.

The version of a UUID is stored in the high nibble of the 13th hex digit (the first digit of the third group): 1 for time-based, 3 for name-based MD5, 4 for random, 5 for name-based SHA-1, 6 for reordered time, 7 for Unix-epoch time, and 8 for vendor-defined. The variant is stored in the high bits of the 17th hex digit (the first digit of the fourth group); RFC 4122 uses the 10xx pattern.

The validator returns the canonical lowercase hyphenated form, the detected version and its name, the variant, and flags for the special nil UUID (all zeros) and max UUID (all f’s). Everything runs in your browser; nothing is uploaded.

Frequently asked questions

How does it tell the UUID version?

The version is the first hex digit of the third group. For example, in 550e8400-e29b-41d4-a716-446655440000 that digit is 4, so it is a version 4 (random) UUID. The validator reports both the number and a plain-English name.

What UUID formats does it accept?

It accepts the standard hyphenated form, a compact 32-character hex string with no hyphens, the urn:uuid: prefix, and a braced {…} form. All are normalized to the canonical lowercase hyphenated form in the result.

What is the nil UUID?

The nil UUID is 00000000-0000-0000-0000-000000000000 — all 128 bits zero. It is a reserved special value used to represent "no UUID". The max UUID is the opposite: every bit set to one.

Does validating a UUID guarantee it is unique?

No. Validation only checks that the format, version and variant bits are well-formed. It does not check that the UUID has never been issued. Uniqueness comes from the generation algorithm, not from the shape.

UUID Validator

Deep dive guides

How uuid validator works

Frequently asked questions

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