ROT13 Encoder / Decoder
Encode or decode text using ROT13, the simple letter substitution cipher that shifts each letter 13 positions.
Commonly used online for spoiler text.
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 — 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 — 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 ROT13 provides zero security. It is a Caesar cipher with a fixed shift of 13. It should never be used to protect sensitive information. Its only purpose is casual obfuscation — making text unreadable at a glance but trivially reversible.