yEnc Decoder

About this calculator

yEnc is a binary-to-text encoding scheme designed specifically to post binary files (images, video, archives) to Usenet more efficiently than older methods. Where Base64 or uuencode inflate a file’s size by roughly 33-40% because they map raw bytes into a restricted printable-ASCII alphabet, yEnc instead shifts each byte’s value by 42 (mod 256) so that most bytes land directly in the printable range, escaping only the handful of bytes (like NUL, LF, CR, and the “=” escape character itself) that would otherwise break line-based text transport — keeping overhead down to roughly 1-2%.

This decoder handles that core “=” escape mechanism, converting a yEnc-encoded string back into text or hex, though it’s simplified and doesn’t parse the =ybegin/=ypart/=yend header lines that a full Usenet binary post uses to specify filename, part number, and CRC checksum. It’s a useful tool for anyone building or debugging Usenet newsreader software, or decoding a yEnc-encoded fragment by hand.