Universally Unique Identifier (RFC 4122 / ISO/IEC 9834-8), a 128-bit value rendered as 32 hexadecimal digits in 8-4-4-4-12 grouping, generated such that the probability of collision across independent generators is negligible.

ByCASRAI Editorial Board

· Last updated 10 Jul 2026

Examples

Worked examples

Is an instance
550e8400-e29b-41d4-a716-446655440000 (a v4 UUID).
Is an instance
urn:uuid:f47ac10b-58cc-4372-a567-0e02b2c3d479 (a UUID expressed as a URN).

Counter-examples

Looks similar, but isn't

Not an instance
An ORCID iD has only 64 bits of randomness in a different format and is not a UUID.
Not an instance
A DOI's suffix is not a UUID.

Editorial commentary

UUIDs come in several variants and versions: v1 (time + MAC), v3 and v5 (namespace + name, hashed), v4 (random), and v7 (time-ordered, RFC 9562). They are widely used as internal database keys, file identifiers, and as URN namespace identifiers (urn:uuid:…). UUIDs are not human-meaningful and are typically opaque; resolution to a useful resource requires an external service or table lookup.

References

Leach P., Mealling M., Salz R., RFC 4122, IETF, 2005.
Davis B., Peabody K., Leach P., RFC 9562, 'Universally Unique IDentifiers (UUIDs)', IETF, 2024.

Also known as

Universally Unique Identifier

Machine-readable encodings

Use in your systems

JATS XML <role> element

xml

<role vocab="credit"
      vocab-identifier="https://casrai.org/dictionary/"
      vocab-term="UUID"
      vocab-term-identifier="https://casrai.org/dictionary/term/uuid" />

Schema.org DefinedTerm (JSON-LD)

json

{
  "@context": "https://schema.org",
  "@type": "DefinedTerm",
  "@id": "https://casrai.org/dictionary/term/uuid",
  "name": "UUID",
  "identifier": "https://casrai.org/dictionary/term/uuid",
  "description": "Universally Unique Identifier (RFC 4122 / ISO/IEC 9834-8), a 128-bit value rendered as 32 hexadecimal digits in 8-4-4-4-12 grouping, generated such that the probability of collision across independent generators is negligible.",
  "inDefinedTermSet": "https://casrai.org/dictionary/domain/persistent-identifiers#set",
  "url": "https://casrai.org/dictionary/term/uuid",
  "sameAs": [
    "Universally Unique Identifier"
  ],
  "license": "https://creativecommons.org/licenses/by/4.0/",
  "publisher": {
    "@id": "https://casrai.org/#organization"
  },
  "dateModified": "2026-07-10T02:06:19",
  "inLanguage": "en"
}

Referenced across the research world

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