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UUID Validator

Check whether a UUID is well-formed and identify its version. For v1 and v7 the embedded creation timestamp is extracted and shown.

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Result
Paste a UUID to check it.

What makes a UUID valid

A UUID is 32 hexadecimal digits in five groups separated by hyphens: 8-4-4-4-12. Two of those digits are not random at all — they encode the version and the variant, and a value with impossible values there is malformed.

The 13th digit is the version, from 1 to 8. The 17th is the variant, which must be 8, 9, a or b for an RFC 9562 UUID.

xxxxxxxx-xxxx-Vxxx-Nxxx-xxxxxxxxxxxx
              ↑    ↑
         version  variant

What each version means

The version digit tells you how the identifier was created, and therefore what it may reveal:

  • v1 — timestamp plus MAC address. Leaks when and on which machine it was made.
  • v3 — MD5 hash of a namespace and name. Deterministic.
  • v4 — entirely random. The general-purpose default.
  • v5 — SHA-1 hash of a namespace and name. Preferred over v3.
  • v7 — Unix millisecond timestamp plus randomness. Sorts chronologically.

The nil and max UUIDs

The nil UUID is all zeros and the max UUID all ones. Both are valid special values defined by the specification. In practice a nil UUID in your data usually means an identifier was never assigned rather than deliberately set.

Frequently asked questions

What makes a UUID invalid?

Wrong length, characters outside 0-9 and a-f, misplaced hyphens, a version digit outside 1-8, or a variant digit that is not 8, 9, a or b. The last two are what distinguish a real UUID from 32 random hex characters.

Are uppercase UUIDs valid?

Yes. The specification says generators should output lowercase but parsers must accept both. This validator normalises to lowercase for comparison.

Can I tell when a UUID was created?

Only for versions 1, 6 and 7, which embed a timestamp. Version 4 is pure randomness and reveals nothing about when it was generated.

Is a UUID without hyphens still valid?

Strictly the canonical form requires them, but the 32-character form is widely used in databases and URLs. This validator accepts it, along with the braced and urn:uuid: forms.

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