The ADFGX cipher was a field cipher used by the German Army during World War I. It is closely related to the ADFGVX cipher. ADFGX is a fractionating transposition cipher which combined a modified Polybius square with a single columnar transposition. The cipher is named after the five possible letters used in the ciphertext: A, D, F, G and X. These letters were chosen deliberately because they sound very different from each other when transmitted via morse code. The intention was to reduce the possibility of operator error.

The alphabet is split into a 5 by 5 matrices arranged in a polybius square. Each of the 5 by 5 matrices contains 25 letters and usually the letter 'j' is merged with 'i' (but you can customize that below to your liking in the "Alphabet Options" section). The ciphertext squares can be generated using a keyword and the remaining spots will be filled with the remaining letters of the alphabet in order. You may also randomly generate both the Alphabet and the Keyword if you wish.