ROT-13 is a special case of the Caesar cipher that rotates each letter 13 places through the 26-letter alphabet. A becomes N, B becomes O, and so on. It is used to lightly hide spoilers or puzzle answers, not for real security.

Why is the same tool used to encode and decode?

Because the alphabet has 26 letters, shifting by 13 twice returns you to the original letter. Applying ROT-13 to already-encoded text decodes it, so there is no separate decode mode needed.

Are numbers and symbols affected?

No. ROT-13 only rotates the 26 letters A to Z in both cases. Digits, spaces, punctuation, and any non-Latin characters pass through completely unchanged.

Not at all. It offers no cryptographic security and can be reversed instantly by anyone. It is meant purely to make text unreadable at a glance, such as hiding a spoiler in a forum post.

ROT-13 Encoder/Decoder

ROT-13 (“rotate by 13 places”) is a simple letter-substitution cipher that shifts each letter 13 positions forward in the alphabet. It is most often used to hide spoilers, puzzle solutions, or punchlines so they are not readable at a glance — never for genuine security.

How it works

Each letter is mapped to the letter 13 positions later, wrapping around the end of the alphabet:

A→N  B→O  C→P … M→Z  N→A … Z→M

Formally, for a letter with zero-based position p in its case, the output position is (p + 13) mod 26. Because 13 + 13 = 26, applying the shift twice returns the original letter — so ROT-13 is its own inverse and one operation both encodes and decodes. Non-letters are left untouched.

Example and tips

The word Hello becomes Uryyb, and running Uryyb through the tool again restores Hello. Case is preserved: uppercase stays uppercase, lowercase stays lowercase. ROT-13 is purely an obfuscation trick — if you need real confidentiality, use a proper cipher or encryption tool instead.