Caesar Cipher & ROT13

What is the Caesar cipher?

A substitution cipher where each letter of the alphabet is replaced by the letter a fixed number of positions later. With a shift of 3, A becomes D, B becomes E and so on; it is one of the oldest known encryption techniques.

How do I use it?

• Choose Encrypt or Decrypt to set the direction of the transformation.
• Drag the shift slider from 1 to 25 to pick how far letters move.
• Hit ROT13 to jump straight to shift 13, where encrypting and decrypting are the same operation.

How a shift cipher works

Every letter moves a fixed number of places down the alphabet: with shift 3, A becomes D and Z wraps to C. The cipher is symmetric — decoding repeats the same shift in the opposite direction, and the shift value is the only secret.

A cipher, not security

There are only 25 meaningful shifts, so a human can break it by hand in minutes and a computer in milliseconds. Treat Caesar as a fun puzzle or a teaching tool, never as protection for real data.

How to use Caesar Cipher & ROT13

Shift your message a few letters forward or backward to make it unreadable at a glance.

Use the controls above to provide your input or choose options, then review the result on the page.

Why use our Caesar Cipher & ROT13

• Encrypts or decrypts text with a Caesar shift from 1 to 25, plus one-click ROT13.
• Complete the task with a focused Caesar Cipher & ROT13 workflow instead of switching between apps.
• Open it in your browser and get started—no account or installation required.