Uuencoding (Unix-to-Unix encoding) is a binary-to-text encoding scheme from the early Unix era. It converts arbitrary bytes to printable ASCII characters so they can be safely transmitted over text-only channels like email or Usenet.

How does uuencoding differ from Base64?

Both are binary-to-text schemes, but uuencoding uses a 6-bit alphabet starting at ASCII 32 (space) and wraps lines at 60 encoded characters. Base64 uses a different 64-character alphabet and is more compact. Base64 has largely replaced uuencoding in modern systems.

What does the number at the start of each line mean?

The first character of each line is a length indicator. It is the number of original bytes encoded on that line, encoded as the byte count plus 32 (to make it printable). For a full line of 45 source bytes, this character is M (ASCII 77 = 45 + 32).

What is the permission mode field?

The three-digit octal number in the "begin" header (e.g. 644) mirrors the Unix file permission that should be applied when the file is decoded. 644 means owner read/write, group and others read-only.

Can this tool handle binary files?

This browser-based tool works with text input. For true binary files (images, executables) you would need to read the raw bytes via the File API. The encoding algorithm itself is identical — only the input method differs.

Is the output compatible with the unix uudecode command?

Yes. The output follows the standard format: "begin " on the first line, encoded data lines, a single backtick or space line, then "end". This is accepted by the uudecode utility on Linux and macOS.

Uuencode Encoder

Paste or type any text and get the Unix uuencoded output with a filename header and standard 60-character line wrapping.

Input Text

Filename

Permission Mode

Uuencoded Output

Encoded output will appear here

Try a Sample

Copied!

Summary

Uuencoding (Unix-to-Unix encoding) is a binary-to-text encoding format originally used to transmit binary files over email and Usenet. This tool converts any plain text or binary data into the standard uuencoded format, wrapping every 45 source bytes into a 61-character encoded line (60 encoded characters plus one length character) and prefixing the output with a "begin" header that carries the filename and permission mode.

How it works

Enter or paste the text you want to encode into the input field.
Optionally set the output filename that will appear in the "begin" header.
Optionally set the Unix permission mode (default 644).
Click "Encode" — the tool groups bytes into 3-byte chunks and maps each chunk to 4 printable ASCII characters.
Each encoded line represents 45 source bytes (60 encoded characters), preceded by a length character.
The output is wrapped in "begin <mode> <filename>" and "end" markers, exactly matching the Unix uuencode format.

Use cases

Prepare text payloads for legacy email systems that require uuencoded attachments.
Test decoders or parsers that consume the uuencode format.
Embed encoded data in shell scripts or Makefiles that call uudecode.
Learn the uuencoding algorithm by comparing raw input with encoded output.
Encode configuration snippets for systems with uudecode but no base64.
Reproduce classic Usenet binary post headers for archival purposes.

Frequently Asked Questions

Last updated: 2026-05-23 · Reviewed by Nham Vu