Q-encoding header encoder

Unlike body quoted-printable, header Q-encoding maps every space to an underscore, forbids soft line breaks inside an encoded-word, and reserves the question mark and underscore so mail parsers never confuse the payload with the =? Use it free in the browser for mail debugging and header practice, or call the API at $0.002 per successful request when pipelines need reproducible RFC 2047 transforms in CI and backend services.

What RFC 2047 Q-encoding is and what this tool returns

An encoded-word looks like equals-question charset question encoding question payload question-equals, where the encoding letter is Q for the quoted-printable-like method or B for Base64. This page always follows that contract for UTF-8 text by default: encode mode maps your string to charset bytes, emits underscore for space and equals-hex for unsafe bytes, then optionally wraps the payload as a full encoded-word; decode mode accepts either a full encoded-word or a bare Q payload, expands underscore and equals-hex pairs, and rejects incomplete or non-hex escape sequences instead of guessing. The JSON response includes result for the transformed string, mode echoing encode or decode, encoding fixed to rfc2047-q, charset, form (encoded_word or payload), the bare payload field for easy assertions, and input_bytes plus output_bytes so you can pin sizes in tests. There is no streaming path and no silent repair of broken Q text: either the string is valid or the request fails with invalid_input.

How text, mode, charset, and form are read and how results stay reproducible

charset? Q? …? Encode accepts Unicode strings, converts them with the chosen charset rules, then emits Q tokens with uppercase hex escapes and underscore for every space. After bytes are recovered, a fatal UTF-8 decode ensures binary garbage does not become mojibake when the charset is UTF-8. The preferred payload field is text, with aliases input, value, and s so forms, query strings, and SDK clients can reuse the same contract without renaming columns. Mode defaults to encode and accepts decode explicitly; aliases op, direction, and action map to the same switch for scripts that already use those names. Charset defaults to UTF-8 and is written into the encoded-word on encode; when decoding a full encoded-word the charset is taken from the token itself, and when decoding a bare payload the charset parameter selects how recovered bytes become text. Form defaults to encoded_word so encode returns a complete =? Decode requires a well-formed Q string: a lone equals at the end of input, an equals followed by one character only, or an equals followed by non-hex digits all fail with a clear invalid_input message naming the malformed escape. Pair the free browser run on this page with the priced API when you need the identical mathematical result inside an automated pipeline without re-implementing RFC 2047 tables yourself. Invalid inputs return invalid_input and are not charged, which keeps validation cheap while successful transforms remain a fixed item price of $0.002.

Where Q-encoding fits in email headers, MIME, and test fixtures

On this page the work runs entirely in your browser; through the API each successful lookup costs $0.002, failed validation is not charged, and nothing is stored after the response returns. That split — free interactive exploration and a priced, identical API — matches the rest of the KIT tier-A catalog and lets you move from a classroom demo to an automated pipeline without changing the encoded result.