The Caesar cipher is one of the oldest encryption tricks in the book — legend has it Julius Caesar used it to send secret military messages over 2,000 years ago. The idea is beautifully simple: shift every letter in your message a fixed number of steps along the alphabet, so 'A' becomes 'D', 'B' becomes 'E', and so on. Use this interactive tool to encode your own secret messages, decode ones sent to you, and discover exactly why this classic cipher is surprisingly easy to crack.
This article and its interactive demo were created with the help of generative AI and editorially reviewed.