UUEncode Encoder & Decoder

UUEncode (Unix-to-Unix encoding) is a way of writing binary data as plain text. It was widely used on Unix systems, in email and on Usenet to send programs and images through channels that only carried text. The result is a block of printable characters, usually wrapped in a “begin” line and an “end” line.

The data is cut into lines of up to 45 bytes. Each group of 3 bytes (24 bits) becomes 4 characters that each carry 6 bits, and every 6-bit value is shown as a printable character by adding 32 to it. Each line starts with a character that gives the number of bytes on the line, and a final line with a backtick marks the end of the data. Zero is written as a backtick instead of a space so that mail systems cannot strip it.

Both turn 3 bytes into 4 characters, but they use different characters. UUEncode uses the printable ASCII range from space to underscore, starts every line with a length character and adds a begin line with a file name and permissions. Base64 uses A–Z, a–z, 0–9, + and /, and has no length characters. With 45 bytes per line UUEncode makes data about 38% larger; Base64 wrapped at 76 characters makes it about 35% larger. A variant called uuencode -m puts Base64 inside a begin-base64 block, and this page can read and write it.

Rarely. Base64 and MIME replaced it for email, and binary attachments or file downloads replaced it on Usenet. You still meet it in old email archives, some mainframe and Unix scripts, and the uuencode and uudecode commands in the sharutils package, so a decoder is useful when you find an old file.

Yes. Text is first turned into UTF-8 bytes, so accents, Indian scripts and emoji survive, and files are read as raw bytes, so images, archives and programs are encoded without damage. When you decode, the result is shown as text if it is valid UTF-8 and otherwise as a hex preview with a button to download the file.

It accepts Windows and Unix line endings, text before the begin line, a missing end line, lines whose trailing spaces were stripped by a mail system, extra characters such as line checksums, several files in one block and the begin-base64 variant. When something looks wrong it decodes what it can and lists warnings, such as a line that is too short or a missing end line, so you can judge the result.

They are checksums of the original data, shown after encoding and after decoding. Compare them with values you compute elsewhere, for example with sha256sum, to confirm that a file survived the trip unchanged. CRC-32 here is the same variant used by gzip and zip. The page also decodes its own output and compares it with your input as a round-trip check.

No. Anyone can decode UUEncoded text, because it only changes how the data is written. If the content is private, encrypt it first and encode the encrypted result.

Files up to 10 MB are accepted for encoding and 20 MB for decoding. Large results are shown as a preview, while Copy and Download always use the full result. For very large files, the uuencode and uudecode command-line tools are faster.

No. Everything runs in your browser, the page’s content security policy blocks outgoing network requests, no outside scripts are loaded, and none of what you enter is saved in cookies or local storage (the page only remembers your chosen site language).