How to Use the Caesar Cipher Encoder & Decoder
A Caesar cipher shifts every letter of the alphabet by a fixed number of positions — one of the oldest known substitution ciphers, said to have been used by Julius Caesar for military messages. Enter your text and a shift value, and in "Encode" mode each letter moves forward by that many positions to create the cipher text; in "Decode" mode the same shift is applied in reverse to recover the original message. With a shift of 3, for example, A becomes D and B becomes E, wrapping back to the start of the alphabet when it runs past Z.
Numbers, spaces, symbols, and non-English characters are left untouched — only English letters (A-Z, a-z) are shifted, preserving case. It's a fun way to trade coded messages with friends, learn how substitution ciphers work in a coding class, or build your own puzzle or escape-room cipher. The shift value can be anywhere from 1 to 25, and entering the same value used to encode will decode the message back to plain text. Everything is calculated instantly in your browser, and nothing you type is ever sent to a server.
Frequently Asked Questions
One of the oldest substitution ciphers, it shifts each letter of the alphabet by a fixed number of positions. It's named after Julius Caesar, who reportedly used it for military messages.
Enter a number from 1 to 25. Using the same shift value for decoding as you used for encoding restores the original text.
This tool only shifts English letters (A-Z, a-z). Numbers, symbols, and other-language characters are left unchanged.