Caesar Cipher Online (Decoder and Encoder)

What is the Caesar cipher?

The Caesar cipher is one of the oldest and simplest encryption techniques. Named after Julius Caesar, who reportedly used it for confidential communication, it shifts each letter of the alphabet by a fixed number of positions.

How it works

With a shift of 3 (the classic “Caesar shift”):

• A becomes D
• B becomes E
• HELLO becomes KHOOR

To decode, you shift letters back by the same amount.

Use this tool

1. Type or paste your text in the left textarea
2. Adjust the shift value (1 to 25) — 3 is the classic default
3. Choose Encode to encrypt or Decode to decrypt
4. The result updates instantly — copy it with the Copy button

The Caesar cipher is no longer used for serious cryptography — modern computers can break it in milliseconds. But it remains a great educational example of substitution ciphers.