{
  "status": "shipping",
  "advantages": [],
  "limitations": [],
  "supersedes": [],
  "supersededBy": [],
  "firstSeen": null,
  "lastSeen": null,
  "updated": "2026-10-17",
  "slug": "zstandard",
  "term": "Zstandard",
  "aliases": [
    "zstd"
  ],
  "definition": "Zstandard is a lossless compression format and codec that stores data in frames with optional external dictionaries and content checksums.",
  "note": "Concatenated frames decode to concatenated output. A valid remaining frame does not prove that an intended later frame is still present. [rfc8878] [hesela-zstd]\n\nSeekable Zstandard adds a seek table in a final skippable frame, allowing a range to be located without decoding the entire preceding stream. Ordinary Zstandard framing does not itself provide that index. [seekable-format]\n\nThe measured CLI experiment distinguishes a checksum stored in a frame from read-time verification: explicitly ignoring the checksum accepted wrong dictionary-derived bytes. Its payload oracle also accepted changed skippable metadata because those bytes were not part of decoded output. [hesela-zstd]\n\nA frame dictionary ID can reject a differently labeled dictionary without a content checksum. Conversely, matching IDs did not detect a controlled dictionary-content mutation in Hesela's formatted-dictionary experiment; the verified content checksum caught that particular mismatch. [hesela-zstd]",
  "related": [
    "compression-dictionary",
    "checksum",
    "backup-verification",
    "transparent-compression",
    "skippable-frame",
    "zstandard-dictionary-id"
  ],
  "citations": [
    {
      "id": "rfc8878",
      "title": "RFC 8878: Zstandard Compression, sections 3.1, 3.1.1.1.3 and 5",
      "url": "https://www.rfc-editor.org/rfc/rfc8878.html",
      "accessed": "2026-10-17"
    },
    {
      "id": "seekable-format",
      "title": "Zstandard seekable format 0.1.0, pinned to v1.5.7",
      "url": "https://raw.githubusercontent.com/facebook/zstd/v1.5.7/contrib/seekable_format/zstd_seekable_compression_format.md",
      "accessed": "2026-10-17"
    },
    {
      "id": "hesela-zstd",
      "title": "Hesela: Compressed archives, dictionary dependencies and validation coverage",
      "url": "https://hesela.com/analyses/compressed-archives-dictionary-dependencies/",
      "accessed": "2026-10-17"
    }
  ],
  "provenance": [
    "Format facts follow RFC 8878 and the seekable extension. The linked experiment measures CLI 1.5.5 behavior on synthetic data, not a compression benchmark."
  ]
}