To use a Caesar cipher, paste your text, choose a shift from 1 to 25 and encode; each letter moves that many places along the alphabet. ROT13 is the special case with a shift of 13, which encodes and decodes with the same setting. It is a puzzle, not real security.
How to use the Caesar Cipher / ROT13
- Paste your text.
- Choose a shift from 1 to 25, or 13 for ROT13.
- Choose Encode or Decode.
- Copy the result.
Worked example
With a shift of 3, “HELLO” becomes “KHOOR”, because H moves to K, E to H, L to O and O to R.
Tips and common mistakes
- To decode, use the same shift with Decode, or the reverse shift with Encode.
- Only letters change; numbers and punctuation stay the same.
- A Caesar cipher is trivially breakable, so use it for games, not secrets.
Frequently asked questions
What is ROT13?
A Caesar cipher with a shift of 13. Applying it twice returns the original text.
Is a Caesar cipher secure?
No. There are only 25 possible shifts, so it can be broken instantly.
Are lower-case letters handled?
Yes. Case is preserved.