{
  "id": "encoding/quoted-printable",
  "family": "encoding",
  "slug": "quoted-printable",
  "title": "Quoted-Printable (RFC 2045 §6.7)",
  "summary": "Quoted-Printable is a MIME content-transfer-encoding that leaves printable US-ASCII bytes (0x21-0x7E except '=') as-is and escapes everything else as '=' followed by two uppercase hex digits, so mostly-text data stays human-readable over 7-bit mail transports. Lines are wrapped at 76 characters using a trailing '=' soft line break, and a literal '=' is always written as '=3D'.",
  "kind": "encoding",
  "aliases": [
    "quoted printable",
    "QP",
    "MIME QP",
    "Content-Transfer-Encoding: quoted-printable"
  ],
  "status": "standard",
  "verification": "verified",
  "tier": "A",
  "source_url": "https://www.rfc-editor.org/rfc/rfc2045#section-6.7",
  "source_version": "RFC 2045 §6.7",
  "retrieved_date": "2026-05-29",
  "see_also": [
    "encoding/base64",
    "encoding/percent-encoding"
  ],
  "ext_type": "encoding@1",
  "ext": {
    "rfc": "RFC2045",
    "charset": "US-ASCII",
    "algorithm": "quoted-printable",
    "notes": [
      "Rule 1 (literal): printable ASCII 0x21-0x7E, EXCEPT '=' (0x3D), is left unchanged.",
      "Rule 2 (escape): any other byte is written as '=' followed by its two-digit uppercase hex value (e.g. an e-acute in UTF-8, 0xC3 0xA9, becomes '=C3=A9').",
      "Rule 3 ('=' is special): '=' itself MUST be encoded as '=3D'; it can never appear literally because it introduces an escape.",
      "Whitespace: SPACE (0x20) and TAB (0x09) may appear literally except at the end of a line, where they must be escaped (=20 / =09) so trailing whitespace survives transport.",
      "Soft line breaks: encoders limit lines to 76 chars by inserting '=' immediately before the CRLF; a decoder drops a '=' that is the last char on a line. This entry's test vectors use the simple (non-wrapped) form."
    ],
    "test_vectors": [
      {
        "input": "Hello",
        "input_form": "ascii",
        "output": "Hello",
        "output_form": "ascii",
        "algorithm": "quoted-printable",
        "direction": "encode",
        "note": "All printable ASCII passes through unchanged."
      },
      {
        "input": "a=b",
        "input_form": "ascii",
        "output": "a=3Db",
        "output_form": "ascii",
        "algorithm": "quoted-printable",
        "direction": "encode",
        "note": "Literal '=' (0x3D) is always escaped to '=3D'."
      },
      {
        "input": "café",
        "input_form": "utf8",
        "output": "cafe=CC=81",
        "output_form": "ascii",
        "algorithm": "quoted-printable",
        "direction": "encode",
        "note": "Combining acute accent U+0301 = UTF-8 0xCC 0x81 -> '=CC=81' (non-ASCII bytes escaped)."
      },
      {
        "input": "100°F",
        "input_form": "utf8",
        "output": "100=C2=B0F",
        "output_form": "ascii",
        "algorithm": "quoted-printable",
        "direction": "encode",
        "note": "Degree sign U+00B0 = UTF-8 0xC2 0xB0 -> '=C2=B0'."
      },
      {
        "input": "100=C2=B0F",
        "input_form": "ascii",
        "output": "100°F",
        "output_form": "utf8",
        "algorithm": "quoted-printable",
        "direction": "decode",
        "note": "Round-trip: QP-decode(\"100=C2=B0F\") = \"100°F\"."
      }
    ]
  },
  "updated": "2026-05-29T00:00:00Z"
}