A cipher that is its own key
ROT13 shifts every letter thirteen places. Since the alphabet has twenty-six, applying ROT13 twice returns the original text. So there is no « encode » button and no « decode » button: it is the same operation. Mathematicians call this an involution, and it is the whole elegance of the scheme.
You can check it right here: the result of the second application is shown next to the first.
ROT5, ROT18, ROT47: what the variants are for
- ROT5 touches digits only, shifted by five. Useful when your text contains numbers that ROT13 leaves alone.
- ROT18 combines both: letters by 13, digits by 5.
- ROT47 covers all 94 printable ASCII characters, punctuation included. The result is unreadable even in shape, which ROT13 is not.
- ROT-N: any shift you like, which is exactly the Caesar cipher.
None of these is encryption. ROT13 hides a puzzle answer, a film ending or a punchline — it does not protect information.
Frequently asked questions
Is ROT13 secure?
No, and it never claimed to be. It has no key: anyone who recognises ROT13 decodes it instantly. It is a polite blindfold, not a lock.
How does it differ from the Caesar cipher?
In principle it does not: ROT13 is the Caesar cipher with the shift fixed at 13. That particular shift is what gives it the involution property.
Does ROT13 change accented letters?
No. Only A-Z and a-z are shifted; accents, digits and symbols stay as they are — except under ROT47, which touches all ASCII punctuation.