{
  "id": "identifier/ulid",
  "family": "identifier",
  "slug": "ulid",
  "title": "ULID (Universally Unique Lexicographically Sortable Identifier)",
  "summary": "A ULID is a 128-bit identifier: a 48-bit Unix-millisecond timestamp followed by 80 bits of randomness, rendered as 26 characters of Crockford's Base32. Because the timestamp is the high-order portion and Base32 preserves order, ULIDs sort lexicographically by creation time. It is UUID-compatible in size (128 bits) but more compact and case-insensitive in text.",
  "kind": "identifier",
  "aliases": [
    "Universally Unique Lexicographically Sortable Identifier"
  ],
  "status": "de-facto",
  "verification": "verified",
  "tier": "B",
  "source_url": "https://github.com/ulid/spec",
  "source_version": "ulid/spec (unversioned)",
  "retrieved_date": "2026-05-29",
  "see_also": [
    "identifier/uuidv7",
    "identifier/ksuid",
    "encoding/base32"
  ],
  "ext_type": "identifier@1",
  "ext": {
    "spec": "ULID spec (github.com/ulid/spec)",
    "example": "01ARZ3NDEKTSV4RRFFQ69G5FAV",
    "bit_layout": [
      {
        "field": "time",
        "bits": 48,
        "meaning": "Unix timestamp in milliseconds; encodes as the first 10 Base32 characters."
      },
      {
        "field": "randomness",
        "bits": 80,
        "meaning": "Cryptographically random; encodes as the last 16 Base32 characters."
      }
    ],
    "length_bits": 128,
    "sortable": true,
    "encoding": "Crockford's Base32 (alphabet 0123456789ABCDEFGHJKMNPQRSTVWXYZ), 26 characters",
    "notes": [
      "26-char string = 10 chars timestamp + 16 chars randomness. Crockford Base32 excludes I, L, O, U to avoid ambiguity; canonical form is uppercase but decoding is case-insensitive.",
      "Lexicographically sortable: the millisecond timestamp is the most-significant field, so string sort == time sort. Monotonic mode increments the random component within the same millisecond to preserve ordering.",
      "128 bits total, so a ULID can be stored in a UUID column; conceptually parallel to UUIDv7 (same 48-bit ms time + randomness split) but with a different text encoding.",
      "Example 01ARZ3NDEKTSV4RRFFQ69G5FAV is the canonical example from the ULID spec."
    ]
  },
  "updated": "2026-05-29T00:00:00Z"
}