How caesar cipher works
The Caesar cipher is one of the oldest known encryption methods, named after Julius Caesar who used a shift of 3. Each letter in the message is replaced by the letter a fixed number of positions down the alphabet. A shift of 3 turns A into D, B into E, and so on, wrapping around so Z becomes C.
To decrypt, you shift each letter back by the same amount. Because there are 26 letters, a shift of 13 (ROT13) is its own inverse — applying it twice returns the original text, which is why ROT13 is popular for hiding spoilers in plain sight. This tool supports any shift value, positive or negative, and treats decrypt as the reverse shift.
Enter your text, choose a shift, and pick encrypt or decrypt. The tool shifts only letters (both cases preserved) and leaves numbers, punctuation, and other characters untouched. The Caesar cipher is a historical toy and is trivially breakable by brute force or frequency analysis — never use it for real security.