This is a simple game to illustrate how basic frequency analysis (which letters occur most commonly in English words) can be used to decode an enrypted message where a basic alphabetic substitution has been used (swapping one letter for another).
The source code is available on github
First choose a random piece of enrypted text to work on
This is the mapping table that holds plain text gueses and their encrypted counterparts. Fill in a guess box and then click "try my guess". Each letter's frequency in English is included in the table so the chances are that the letter in the encrypted text that appears the most often is "e", and so on.