The Polybius square writes the alphabet into a grid, and each letter becomes its row and column number: h is 23, i is 24. The English square is 5 × 5 with I and J sharing a cell; the Russian one is 6 × 6. A keyword shuffles the square, and without it the ciphertext cannot be read.
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Diagram
5 × 5 square
123451ABCDE2FGHI/JK3LMNOP4QRSTU5VWXYZ
Letters of your text are highlighted. Row — column.
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How it works
Row and column
h = 23 · i = 24
The alphabet is written into the square row by row. The first digit is the row, the second the column.
A keyword
z e b r a c d …
The keyword's letters without repeats take the first cells and the rest follow. Without it the square cannot be rebuilt.
I and J together
25 cells, 26 letters
The English square is 5 × 5, so I and J share a cell. The Russian one is 6 × 6: 33 letters and 3 signs.
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Frequently asked questions
The letters of the alphabet are written into the square row by row, and each letter of the text is replaced by two digits: its row and its column. Hello in the English 5 × 5 square is 23 15 31 31 34. To decode, find the cell where each pair of numbers crosses. The square on this page highlights the letters of your text.
A 5 × 5 square has 25 cells and the English alphabet has 26 letters, so two of them must share. By tradition I and J go together, and decoding gives i where j was written; the meaning is rarely lost. The Russian alphabet has 33 letters, so its square is 6 × 6: 33 letters and three cells for the full stop, comma and hyphen.
Type the keyword into the Keyword box: its letters without repeats fill the first cells, and the rest of the alphabet follows in order. With the keyword zebra the square starts z, e, b, r, a, c. Whoever knows the keyword builds the same square and decodes the text; without it, the number pairs point to the wrong letters.
Switch to Decode and paste the pairs of digits, with spaces or run together: 2324 is read as 23 and 24. A slash separates words. A pair that is not in the square, such as 77, becomes a question mark and is listed above the result. If the text was encoded with a keyword, enter the same keyword, or the letters come out wrong.
The Greek historian Polybius, in the second century BC, described signalling letters with torches: the number of torches in the left and right hand gave the row and column of a table. Prisoners' tap code through a wall uses the same idea, and in the First World War the square was the base of the German ADFGVX cipher, combined with a transposition.
Nowhere. The square is built and applied in your browser, and the text and keyword stay on your device and are not written into the page address. If you want to send a puzzle, the Share button builds a link, and the note beside it says what goes in, keyword included. Statistics see only that the tool was used.