Caesar Cipher Tool

It is one of the oldest known encryption methods, named after Julius Caesar who reportedly used it in his private letters. Every letter in the message is replaced by the letter a fixed number of positions further along the alphabet (wrapping back to A after Z), and that fixed number is called the shift.

ROT13 is just a Caesar cipher with the shift fixed at 13. Since the alphabet has 26 letters, shifting by 13 twice lands you back exactly where you started, which makes ROT13 self-inverse: the same operation both encrypts and decrypts. That property made it a popular, simple way to hide spoilers or punchlines in old forum posts, since running the same "cipher" again reveals the text.

Since there are only 25 possible non-zero shifts, the brute-force list simply tries every single one and decodes your text with each, so the correct shift's result is always sitting somewhere in that list as readable text; you just scan down and recognize it.

It counts how often each letter A through Z appears in your text. A Caesar cipher only shifts letters, it never changes how often each one appears relative to the others, so the shape of the frequency chart for an encrypted message is identical to the shape for the original message, just relabeled. In English, the tallest bars almost always end up on E and T, which is exactly the classic weakness that lets someone crack a Caesar cipher without ever knowing the shift.

No, not by modern standards. With only 25 possible shifts to try, it offers no real protection against anyone who bothers to check; it is included here purely as a classic educational cipher and a fun way to obscure text casually, not as a way to protect sensitive information.