ROT-X allows you to encrypt plain text. "X" refers to a variable number of letters to shift. The most famous is ROT13, in which each letter is shifted halfway through the alphabet. And there is a ROT13 font that makes it easy to see and use.
ROT-X is simple to decrypt, because to undo the first rotate (ROT is short for rotate), you should rotate again by 26 - X. So a ROT13 will reverse a ROT13, a ROT6 will reverse a ROT20, etc.
This page could also be called ROT-N, where N (or n) is any number of times to shift the letters. But the page would be pronounced as "rotten", so "rot-x" sounds better.
Enter a number in the ROT- field, enter a phrase in the Phrase field, and then click the button to encrypt the text.
QMKC DSL QGRC RNLD ETM RHSD SOME FUN SITE TPNF GVO TJUF UQOG HWP UKVG VRPH IXQ VLWH WSQI JYR WMXI