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.

FAQ

• Which characters are changed? Only A–Z and a–z are shifted; numbers, accents, Turkish letters and symbols stay untouched.
• Is ROT13 secure? No, it is not a form of real encryption — like all Caesar shifts it is trivially breakable.
• Where is the work done? Entirely in your browser; your text is never uploaded.

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.