A simple puzzle tool
This is a little encrypter/decrypter widget for an English-alphabet Caesar cipher (or "shift cipher") which transforms a piece of text by "rotating" all the alphabetic characters to a different position in the alphabet by a particular offset amount. (The tool ignores any non-alpha characters.)
Since decryption is performed by the same operation as encryption but with a different offset, you can click the "Invert" button to quickly swap to the mod-26 complement of the current rotation value.
If you THINK you have a Caesar ciphertext but you aren't sure, or know that you have one but you aren't sure what the offset is, you can hit the Auto-Decipher button. This determines the output for every possible rotation value and, using monogram frequencies for English text, applies the offset it considers the most likely to produce an English string.