{
  "id": "identifier/uuidv1",
  "family": "identifier",
  "slug": "uuidv1",
  "title": "UUID Version 1 (Gregorian time + node)",
  "summary": "UUIDv1 is a 128-bit time-based UUID: a 60-bit timestamp counting 100-nanosecond intervals since 1582-10-15 00:00:00 UTC (the Gregorian calendar epoch), a 14-bit clock sequence, and a 48-bit node identifier (historically the host MAC address). The time field is split across three sections, so v1 strings are NOT lexicographically time-sortable; UUIDv6 reorders the same data to fix that.",
  "kind": "identifier",
  "aliases": [
    "UUID v1",
    "time-based UUID",
    "version 1 UUID"
  ],
  "status": "standard",
  "verification": "verified",
  "tier": "B",
  "source_url": "https://www.rfc-editor.org/rfc/rfc9562#section-5.1",
  "source_version": "RFC 9562 §5.1",
  "retrieved_date": "2026-05-29",
  "see_also": [
    "identifier/uuidv4",
    "identifier/uuidv7",
    "identifier/uuid-nil"
  ],
  "ext_type": "identifier@1",
  "ext": {
    "spec": "RFC 9562 §5.1",
    "example": "c232ab00-9414-11ec-b3c8-9f6bdeced846",
    "bit_layout": [
      {
        "field": "time_low",
        "bits": 32,
        "meaning": "Low 32 bits of the 60-bit Gregorian timestamp (100-ns intervals since 1582-10-15)."
      },
      {
        "field": "time_mid",
        "bits": 16,
        "meaning": "Middle 16 bits of the timestamp."
      },
      {
        "field": "ver",
        "bits": 4,
        "meaning": "version = 0b0001 (1)."
      },
      {
        "field": "time_high",
        "bits": 12,
        "meaning": "High 12 bits of the timestamp."
      },
      {
        "field": "var",
        "bits": 2,
        "meaning": "variant = 0b10 (RFC 9562 / former RFC 4122)."
      },
      {
        "field": "clock_seq",
        "bits": 14,
        "meaning": "Clock sequence, to avoid collisions when the clock is set backwards or the node changes."
      },
      {
        "field": "node",
        "bits": 48,
        "meaning": "Node id; historically the 48-bit IEEE 802 MAC address, may be a random multicast-bit-set value for privacy."
      }
    ],
    "length_bits": 128,
    "sortable": false,
    "encoding": "hex with dashes (8-4-4-4-12)",
    "notes": [
      "The 60-bit timestamp is scattered (time_low / time_mid / time_high), so byte order does NOT match time order; v1 is not sortable. UUIDv6 (RFC 9562 §5.6) is the field-compatible, time-ordered re-lay-out.",
      "The example c232ab00-9414-11ec-b3c8-9f6bdeced846 is the RFC 9562 Appendix worked example; the version nibble (13th hex char) is '1' and the variant nibble begins '10' (here 'b').",
      "Embedding the MAC address leaks the host; RFC 9562 permits a random node id with the multicast bit set instead."
    ]
  },
  "updated": "2026-05-29T00:00:00Z"
}