Quoted-Printable encode

Email. It is the RFC 2045 content transfer encoding that keeps mostly-text messages readable while making sure nothing outside plain printable ASCII survives a mail server that only handles seven-bit data. Compared with Base64 it leaves English text legible, which is why mail clients still use it for message bodies.

Printable ASCII from exclamation mark through tilde, except the equals sign, plus the space and the tab. Everything else becomes an equals sign followed by two uppercase hex digits, so a non-breaking space becomes =C2=A0 and the equals sign itself becomes =3D.

Those are soft line breaks. The encoder starts a new line before the output would pass 75 characters and marks the break with an equals sign followed by a carriage return and newline. A decoder removes them, so they do not appear in the final text. Every line in the output is therefore short by design.

They are encoded, not preserved. A newline byte is not in the literal set, so it comes out as =0A and a carriage return as =0D. That means this tool treats your input as a byte stream rather than as lines of text, which is worth knowing if you are comparing its output against a mail client.

No. Spaces and tabs are written as-is wherever they occur, including immediately before a soft break, so a trailing space is not turned into =20. Some mail transports strip such spaces, so check the result if trailing whitespace is significant to you.

No. Encoding is done in a Web Worker in your browser, so the message text you drop in never leaves the tab. That matters here because Quoted-Printable input is usually the body of a real email. There is no upload, no log and no copy kept once you close the page.