Polybius square decoder
Turn Polybius square numbers back into text to solve puzzles. It is a puzzle cipher, not a security tool.
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Processing and privacy: The result is calculated inside your browser and your data is not sent to any server.
How to use it
- Enter numbers.
- The result appears straight away and updates as you edit.
- Copy the result, or copy a link that keeps the same values to share it.
How it is calculated
Each two digits are the row then the column in the square ABCDE / FGHIK / LMNOP / QRSTU / VWXYZ; letter = cell ((row - 1) × 5 + column).
Example
Result: Decoded text: HELLO WORLD; Letters: 10.
23 15 31 31 34 / 52 34 42 31 14
HELLO WORLD
Limits and caveats
- This is a puzzle and teaching cipher that is easy to break, so never use it to protect passwords or sensitive data.
- Code 24 always shows as I, though it may have been J.
Questions about this tool
Do I need spaces between pairs?
No. Every two digits in a row are read as one letter; spaces are only for readability.
Why an error about digits 6 to 9?
The square is 5×5, so there is no row or column past 5. A 0 or 6 to 9 means the text has an error.
Does it support a keyword square?
No. It uses the standard square in alphabet order.