Caesar cipher and ROT13
Encode and decode messages with the Caesar cipher, choosing the shift, or use ROT13. It also shows all 25 attempts to crack the cipher.
Type the message to encrypt.
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Caesar cipher and ROT13: what it is for
Type the message, choose the shift and see the ciphertext instantly. To decrypt, use the same shift in Decrypt mode or try all 25 shifts and find the sentence that makes sense.
The ROT13 button applies a 13-letter shift, widely used to hide spoilers and answers.
How to use
- Type the message.
- Choose encrypt, decrypt or try all.
- Adjust the shift and copy.
When to use it
- Creating puzzles and treasure hunts.
- Studying cryptography at school.
- Hiding spoilers with ROT13.
Frequently asked questions
How does the Caesar cipher work?
Each letter is replaced by the letter a fixed number of positions ahead in the alphabet. With a shift of 3, A becomes D, B becomes E and so on, wrapping back to the start after Z.
What is ROT13?
It is the Caesar cipher with a shift of 13. Since the alphabet has 26 letters, applying ROT13 twice gives you back the original text.
Is the Caesar cipher secure?
No. There are only 25 possible shifts, so you can just try them all, as the brute-force option does. Use it only for fun, study and puzzles.
Is it really free?
Yes, 100% free. No sign-up, no subscription and no usage limits. All Tools123 tools are free and run right in your browser.