Free tool
Caesar Cipher and ROT13
Encrypt a text by shifting each letter a number of positions, decrypt it, or try every shift to break an encrypted message.
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Characters: 0 · Lines: 0
Everything is processed in your browser. What you type is not sent to any server or stored.
How it works and what it does with your text
It's a small, straightforward utility: you paste, choose options and copy the result.
It runs in your browser
The text is transformed by this page's code, on your device. No sign-up or installation needed.
We don't store what you type
We don't send your text to any server or store it. You can check this in the Network tab of your browser's developer tools.
Free and unlimited
Use it as often as you like. It works the same on mobile and on desktop.
Tips to get the most out of it
How it works
Each letter is replaced by the one N positions further along the alphabet: with a shift of 3, A becomes D and X becomes A. Accents, digits and symbols don't change.
ROT13
It is Caesar with a shift of 13. With 26 letters, you decrypt it by applying it again, and it is used to hide spoilers or answers in forums. It protects nothing.
Breaking a message
There are only 25 possible shifts, so “Try all 25 shifts” shows you all of them and you just have to read which one makes sense.
Spanish alphabet
For texts with ñ choose the 27-letter alphabet: the ñ sits between n and o. You must use the same alphabet to encrypt and decrypt.
Frequently asked questions
What is the Caesar cipher?
It is one of the oldest ciphers: it shifts each letter a fixed number of positions in the alphabet. It is attributed to Julius Caesar, who used a shift of 3.
How do I decrypt a Caesar message without knowing the shift?
Use “Try all 25 shifts” and look for the line that makes sense. It also works for ROT13.
Is the Caesar cipher secure?
No: there are only 25 possible keys and it is broken in seconds. It is a teaching exercise or a game; to really protect information use AES.
What is the difference between ROT13 and Caesar?
ROT13 is a Caesar with a fixed shift of 13. Since the English alphabet has 26 letters, encrypting and decrypting are the same operation.
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