ROT13 Encoder / Decoder

What Is ROT13? ROT13 (Rotate by 13) is a simple letter substitution cipher that replaces each letter with the letter 13 positions after it in the alphabet. Because the English alphabet has 26 letters, applying ROT13 twice returns the original text, so encoding and decoding are the same operation.

How It Works A becomes N, B becomes O, C becomes P, and so on. The mapping is: A-M maps to N-Z, and N-Z maps back to A-M. Numbers, punctuation, and spaces are not changed. Only the 26 English letters are rotated.

The Complete Mapping ABCDEFGHIJKLM maps to NOPQRSTUVWXYZ. NOPQRSTUVWXYZ maps to ABCDEFGHIJKLM. For example, “HELLO” becomes “URYYB”.

History and Usage ROT13 became popular on Usenet newsgroups in the 1980s as a way to hide spoilers, punchlines, and potentially offensive content. It was never intended as real encryption, and it is trivially easy to reverse. The convention allowed readers to choose whether to decode the hidden text.

ROT13 in Internet Culture ROT13 is still used online today for hiding spoilers in forums and comments. Some websites offer ROT13 encoding as a feature. It has become an inside joke in programming culture. “ROT26 encryption” (applying ROT13 twice, which does nothing) is a well-known programmer joke. Another joke is using “triple ROT13” for “extra security.”

Not encryption, and never was ROT13 provides zero security. It is a Caesar cipher with a fixed shift of 13, the key is public, and there is nothing to guess. It should never be used to protect anything.

Its purpose is consent. Hiding a punchline behind ROT13 does not stop anyone reading it; it stops them reading it by accident, which is a completely different problem and one that a real cipher would solve badly. That is why the convention survived thirty years of better tools existing.