ROT13 Cipher

A Caesar cipher with fixed shift of 13 that is its own inverse for the 26-letter Latin alphabet.

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A Caesar cipher with fixed shift of 13 that is its own inverse for the 26-letter Latin alphabet.

ROT13 replaces each letter with the letter 13 positions after it in the alphabet, wrapping around: A↔N, B↔O, C↔P, ..., M↔Z. Because 13 is exactly half of 26, applying ROT13 twice returns the original text — the cipher is its own inverse. Case and non-letter characters are left unchanged. ROT13 provides essentially no cryptographic security; it is used as a light obfuscation to hide spoilers, punchlines, or mild offensive material.

E(x) = (x + 13) mod 26, applied letter-by-letter

HELLO → URYYB
CLAUDE → PYNHQR
ROT13(ROT13(x)) = x

How to recognize it

Every letter is shifted by the same amount
Applying the transformation twice returns the original
A↔N, B↔O, C↔P are the classic letter pairs

Common mistakes

Confusing ROT13 with atbash (which reverses the alphabet A↔Z, B↔Y, ...)
Applying the shift to digits or punctuation
Shifting by 12 or 14 instead of exactly 13

Practice guidance

Coding & Decoding