Playfair Cipher

How to use

1. 1Choose Encode to encrypt plain text or Decode to decrypt Playfair cipher text.
2. 2Enter a keyword. It fills the 5x5 square first (duplicates removed), then the rest of the alphabet, and both sides must use the same keyword.
3. 3Pick the square variant: merge I and J into one cell, or omit Q. Adjust the padding letter if you do not want the default X.
4. 4Type or paste your text. Spaces, digits, and punctuation are stripped, and the cleaned letters are split into pairs automatically.
5. 5Read the result, watch the key square highlight the active pair, and open the digraph breakdown to see the rule applied to each pair.
6. 6Use Send to decode or Send to encode to round-trip the text, then copy the result, grouped into pairs or as a solid string.

About this tool

Playfair Cipher encrypts and decrypts text with the first practical digraph substitution cipher, invented by Charles Wheatstone in 1854 and championed by Lord Playfair, who gave it his name. Instead of substituting one letter at a time, it works on pairs of letters using a 5x5 key square, which flattens the single-letter frequencies that make a Caesar or simple substitution cipher easy to break by hand, and it saw real field use by the British in the Boer War and the First World War. This tool builds the square from a keyword you choose: the keyword letters fill the grid first with duplicates removed, then the rest of the alphabet follows in order. Because a 5x5 grid holds only 25 letters, one letter of the alphabet has to share a cell or be dropped, and the tool supports both common conventions. The default merges I and J into one cell (the classic textbook choice), and the alternative omits Q (mapping any Q in your text to K). Encryption splits the cleaned text into pairs and applies three rules: two letters in the same row each shift one place to the right, two letters in the same column each shift one place down, and any other pair forms a rectangle where each letter keeps its row but swaps to the other letter's column. Decryption reverses the row and column shifts and uses the identical rectangle rule. A doubled letter such as the pair in the word balloon cannot be encrypted, so the cipher inserts a padding letter (X by default, configurable) between them, and a lone final letter is padded the same way so every pair has two different letters. The live key square shows the exact grid in use and highlights the first pair being processed, and a digraph breakdown lists every pair, the letters it produced, and which of the four rules (same row, same column, rectangle, or padded) was applied, so you can follow the transformation step by step or check homework by hand. You can group the output into space-separated pairs the way Playfair output is traditionally written, swap the result back into the input to verify a round trip, and copy the result with one click. The Playfair cipher is a historical and recreational cipher: it resists casual frequency analysis but is broken quickly by modern cryptanalysis, so it belongs to learning, classwork, capture-the-flag challenges, escape rooms, and puzzle hunts rather than protecting real secrets. Everything runs locally in your browser, so the text and keyword you enter are never uploaded.

Free to use. Works in your browser. No signup, no login.