This cracker uses a method called frequency analysis for people who want to sound cool, or counting letters for simpler folk. Basically, we count the number of letters (and spaces) in your string of text, and then compare them to either the standard distribution of letters in english OR, the distribution of a user inputted block of text. Then it replaces the ciphertext with its realtext counterpart. Because of this, there can be 'incomplete' cracks, where most letters are correct but a few are off.
Put your ciphertext in the box on the top. If you want to use the standard distribution of english, or don't have a larger sample, leave the bottom box empty. If you have a large sample of words from the same writer, paste it in the bottom box. Make sure your sample is long enough that it uses all the letters several times.