Softonic

Polybius Cipher Encoder

Step 1 / 2

5×5 grid; I and J share cell 24. Word separator: /

Next

Convert Latin letters with a fixed 5×5 Polybius square. The encoder maps A–Z to row-column pairs, with I and J sharing 24, writes / for whitespace, and drops other characters. The decoder accepts space-separated pairs and / word separators. This is a learning and puzzle tool, not secure encryption.

How to use this Polybius tool

  1. 1

    Choose encode or decode

    The tool always uses the fixed 5×5 alphabet shown below; there is no keyed or 6×6 mode.

  2. 2

    Enter compatible text

    For encoding, use unaccented Latin letters. For decoding, separate every two-digit coordinate with a space and use / between words.

  3. 3

    Copy the result

    Encoding uses row first, then column. Decoding ignores tokens that are not valid cells.

The grid used by the tool

    1   2   3   4   5
1   A   B   C   D   E
2   F   G   H  I/J  K
3   L   M   N   O   P
4   Q   R   S   T   U
5   V   W   X   Y   Z

The first digit is the row and the second is the column. Therefore C = 13, T = 44, and HELLO = 23 15 31 31 34. Both I and J encode as 24. In this implementation, decoding 24 produces J, so a decoded message cannot recover whether the source contained I or J.

Exact input rules

The encoder converts text to uppercase, maps only the letters A–Z, and turns each whitespace character into /. Punctuation, digits, emoji and accented letters are omitted. The decoder reads tokens separated by whitespace: 23 24 / 44 23 15 42 15 becomes HJ THERE. A token such as 2315, 00 or punctuation is ignored rather than reported as an error.

What Polybius is good for

The square is useful for classical-cipher lessons, hand signals and puzzle design. It is a monoalphabetic substitution, so it does not protect sensitive information. This version does not support keywords, custom alphabets, a 6×6 letter-and-digit square, or automatic separator detection.

Data handling

This is a server-backed tool: the text you enter is sent to this site’s server to calculate the result. In the two-step view it is also temporarily stored in your browser’s session storage so it can be restored between steps. No third-party cipher service is contacted, but you should not enter secrets.

Frequently Asked Questions

I and J both map to cell 24, and this implementation chooses J when reversing that shared cell. The original letter cannot be inferred from the coordinates alone.

No. Put a space between every pair, such as 23 15 31 31 34. Use / as a separate token for a word space.

No. Encoding keeps A–Z and converts whitespace to /. Other characters are dropped.

No. Polybius is suitable for education and puzzles, not passwords, private messages or other sensitive data.

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Tool available in other languages