ROT13 Encoder/Decoder

How to use ROT13 Encoder/Decoder

1. Type or paste your text.
2. The rotated text appears immediately.
3. To decode, paste the rotated text in — the operation is its own inverse.
4. Only A–Z and a–z are affected; numbers, punctuation and other scripts are untouched.
5. Applying it twice returns the original text exactly.
6. Everything runs in your browser.

What it does and does not touch

Letters rotate: A becomes N, N becomes A, a becomes n. Case is preserved. Digits, spaces, punctuation and every non-Latin character pass through unchanged, which is why ROT13 text is instantly recognisable — the word shapes and punctuation survive, so it reads as plausible gibberish rather than as random bytes. The classic demonstration is that “WKXKXKX” and “JXKXKXK” are each other’s ROT13.

It is not encryption, and was never meant to be

There is no key. Anyone who recognises ROT13 can reverse it, and a computer can break it instantly by trying all 25 rotations. Its actual purpose, on Usenet from the early 1980s onward, was social: hiding a spoiler, a punchline or an offensive joke behind one deliberate step, so that reading it was a choice. It is a politeness convention wearing the costume of a cipher, and using it to protect anything real is a well-known category error.

ROT13 and the Caesar cipher family

ROT13 is the Caesar cipher with a shift of thirteen. Caesar reportedly used a shift of three; any shift from 1 to 25 works the same way, and all are broken by frequency analysis or simple brute force. Thirteen is special only because it is self-inverse, which saves having separate encode and decode functions. The variant ROT47 extends the idea across 94 printable ASCII characters, so it scrambles digits and punctuation too — and is equally unprotective.