Caesar Cipher
Encode and decode text using the Caesar cipher. Shift each letter by a fixed amount (shift 13 = ROT13). Supports encode and decode modes; non-letters pass through unchanged.
Input
Shift 13 = ROT13
Output
Guides
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 to protect messages of military significance. It is a substitution cipher: every letter in the text is replaced by a letter a fixed number of positions further along the alphabet. With a shift of 3, A becomes D, B becomes E, and so on — wrapping around at the end, so Z becomes C.
How this tool works
- Type or paste your text into the Input Text box.
- Pick a Shift Amount between 1 and 25.
- Choose Encode to encrypt or Decode to reverse a shift.
The result updates automatically as you type. Letter case is preserved, and anything that isn't a letter — numbers, punctuation, spaces, emoji — passes through unchanged.
ROT13
A shift of 13 is the well-known ROT13 variant. Because the Latin alphabet has 26 letters, applying ROT13 twice returns the original text — encoding and decoding are the same operation. ROT13 is still used online to hide spoilers or puzzle answers from a casual glance.
Is the Caesar cipher secure?
No — with only 25 possible shifts it can be broken instantly by trying them all, and even faster with letter-frequency analysis. Use it for puzzles, teaching, geocaching and fun, never for protecting real secrets. For actual encryption, use modern algorithms such as AES.
Privacy
This tool runs entirely in your browser. Your text is never uploaded to a server.