One of the oldest known substitution ciphers: it shifts every letter of the alphabet by a fixed number of positions to encrypt or decrypt. Don't know the shift? Brute-force mode shows all 25 possibilities at once.
⚠️ Educational/puzzle tool only — do not use this for real security purposes.
The Caesar cipher is named after Julius Caesar, who reportedly used a shift of 3 to protect military communications in ancient Rome. It's one of the oldest documented substitution ciphers, and its simplicity has made it a staple teaching example ever since.
The cipher shifts each letter of the alphabet by a fixed number of positions (the shift, or key). With a shift of 3, A becomes D, and letters near the end wrap around — Z becomes C. The same key is used for both directions: to decrypt, you simply shift by the negative amount (-N) to undo the encryption.
There are only 25 possible shifts, so trying every one of them — exactly what this tool's brute-force mode does — cracks any Caesar-ciphered message almost instantly. Frequency analysis works just as fast. That makes the Caesar cipher strictly a tool for education and puzzles, never for protecting anything you actually care about keeping secret.