{
  "id": "identifier/uuid-nil",
  "family": "identifier",
  "slug": "uuid-nil",
  "title": "Nil UUID (all-zero)",
  "summary": "The Nil UUID is the special UUID with all 128 bits set to zero: 00000000-0000-0000-0000-000000000000. RFC 9562 defines it as a sentinel meaning 'no UUID' / absent value. Its version and variant nibbles are both zero, so it does not match any real version's bit pattern.",
  "kind": "identifier",
  "aliases": [
    "nil UUID",
    "null UUID",
    "zero UUID",
    "empty GUID"
  ],
  "status": "standard",
  "verification": "verified",
  "tier": "B",
  "source_url": "https://www.rfc-editor.org/rfc/rfc9562#section-5.9",
  "source_version": "RFC 9562 §5.9",
  "retrieved_date": "2026-05-29",
  "see_also": [
    "identifier/uuid-max",
    "identifier/uuidv4"
  ],
  "ext_type": "identifier@1",
  "ext": {
    "spec": "RFC 9562 §5.9",
    "example": "00000000-0000-0000-0000-000000000000",
    "bit_layout": [
      {
        "field": "all_zero",
        "bits": 128,
        "meaning": "Every bit is 0. Version nibble = 0 and variant nibble = 0, so it is not a valid v1-v8 value."
      }
    ],
    "length_bits": 128,
    "sortable": false,
    "encoding": "hex with dashes (8-4-4-4-12)",
    "notes": [
      "Sentinel for 'no UUID' / unset; sorts before every other UUID.",
      "Counterpart of the Max UUID (all ones). Both are reserved special forms in RFC 9562 §5.9 / §5.10."
    ]
  },
  "updated": "2026-05-29T00:00:00Z"
}