Polybius Square Cipher
Choose encoding or decoding, enter text, and convert it locally in your browser.
A QUICK WALKTHROUGH
How to use this tool
- Choose Encode or Decode.
- Enter letters, coordinate pairs, spaces, or punctuation.
- Convert and copy the local result if needed.
Defined square and preservation rules
The square is A B C D E / F G H I/J K / L M N O P / Q R S T U / V W X Y Z. Encoding maps letters to row-column pairs from 11 to 55, treats J as I, and leaves spaces and punctuation unchanged. Decoding reads valid pairs and leaves non-digit characters unchanged.
Local text conversion
The conversion runs in your browser. No text is uploaded or stored by this page. Decode input must use complete pairs from 11 through 55; an incomplete or invalid digit pair is reported.
GOOD TO KNOW
Common questions
What happens to J?
J shares the I cell, so both encode to 24 and decode back as I.
Are spaces and punctuation removed?
No. Encoding preserves them, and decoding preserves non-digit characters.
Does this provide modern encryption?
No. Polybius is a historical substitution cipher and should not protect sensitive information.