Caesar Cipher

A free online Caesar cipher tool that shifts each letter in your text by a fixed number of positions through the alphabet. Named after Julius Caesar — who used a shift of 3 to protect military correspondence — this is one of the oldest and simplest encryption methods, making it a staple of introductory cryptography courses and CTF puzzle challenges. Set the shift key (1–25) and every letter moves that many places forward: with a shift of 3, A becomes D, HELLO becomes KHOOR. To decrypt, apply the same shift in reverse. The tool handles uppercase and lowercase separately and leaves numbers and symbols untouched. A brute-force mode cycles through all 25 possible shifts at once, displaying every candidate plaintext side by side — invaluable when you don't know the key and need to eyeball which result reads like real language. This brute-force approach works precisely because Caesar's design is weak by modern standards: with only 25 possible keys, a human can crack it in seconds. That makes it an excellent teaching tool for understanding why stronger ciphers like AES replaced classical substitution. Use it to build escape-room clues, add hidden messages to games, teach the fundamentals of symmetric encryption, or analyze historical ciphers. Nothing leaves your browser.