Encode or decode text with ROT13. Use the slider to pick any shift value from 1 to 25 (ROT-N), or switch to ROT47 mode to rotate letters, digits, and symbols all together.
This is an educational/puzzle tool — do not use it for real security purposes.
In ROT47 mode the shift is locked to 47 and the slider above is disabled.
ROT13 became a familiar fixture on early internet forums and Usenet, used to lightly obscure spoilers, puzzle answers, or off-color jokes so nobody stumbled onto them by accident. Because anyone curious enough could decode it in seconds, it was never meant as real secrecy — just a courtesy shield — and it still shows up today wrapping spoiler text in online communities.
ROT13 is simply the Caesar cipher with its shift locked at 13. Since the Latin alphabet has exactly 26 letters, shifting twice by 13 lands you right back where you started. That makes encoding and decoding the exact same operation — a property that holds only because 13 is precisely half of 26, which is why other ROT-N shifts don't share it unless N happens to equal 13.
Instead of rotating only the 26 letters, ROT47 rotates all 94 printable ASCII characters (codes 33 through 126) by 47 positions. That means digits and punctuation get scrambled too, which is why it was a popular way to lightly obfuscate things like email addresses in plain-text posts back on old Usenet and forums.