ROT13 & Caesar Cipher Tool
Encode or decode text with ROT13 or any Caesar cipher shift from 1 to 25. See all 25 shifts at once to crack a message. Free and instant.
Caesar cipher and ROT13
How to use the ROT13 / Caesar Cipher
- Type or paste your message.
- Leave the shift at 13 for ROT13, or choose any shift from 1 to 25.
- Choose Encode to shift letters forward or Decode to shift them back.
- To crack a message with an unknown shift, click Show all 25 shifts and look for the readable line.
Frequently asked questions
What is ROT13?
ROT13 is a Caesar cipher with a shift of 13. Because the alphabet has 26 letters, applying ROT13 twice returns the original text, so the same step encodes and decodes.
What is a Caesar cipher?
A Caesar cipher replaces each letter with the one a fixed number of places further along the alphabet. With a shift of 3, A becomes D and Z wraps around to C.
Is a Caesar cipher secure?
No. There are only 25 possible shifts, so anyone can try them all in seconds. It is for puzzles and games, never for protecting real information.
What happens to numbers and punctuation?
They are left unchanged. Only the letters A to Z are shifted, and upper and lower case are kept.
How do I decode a Caesar cipher when I do not know the shift?
Click Show all 25 shifts. Exactly one line will read as normal text.