ROT13 Encoder and Decoder

In short ROT13 rotates each letter thirteen places through the alphabet, so A becomes N and N becomes A. Because thirteen is exactly half of twenty-six, applying it twice returns the original — the same operation both encodes and decodes, which is the whole reason it survived. "Hello" becomes "Uryyb" and "Uryyb" becomes "Hello". It is not encryption and was never intended as any. It hides text from an accidental glance and nothing more; anyone can undo it in a second, and any computer can undo it instantly. Its actual purpose was social: on Usenet it was the convention for hiding spoilers, punchlines and answers, so that reading them required a deliberate act rather than an accident. That convention is still occasionally used in forums. For anything that needs to stay hidden, use real encryption — the site's AES tools do that properly. Non-letters pass through untouched, so numbers, punctuation and spacing are unchanged, which is why ROT13 text keeps its shape and is instantly recognisable as ROT13.