~xragoerj: rot13

Yes, there's a functionally identical page at rot13.com. Be careful if you go there; it's a back-end implementation with a glaring XSS hole.

Experience the awesome power of rot13 right here, with no risk:

/rot ther'teen/ [Usenet: from "rotate alphabet 13 places"], v. The simple Caesar-cypher encryption that replaces each English letter with the one 13 places forward or back along the alphabet, so that "The butler did it!" becomes "Gur ohgyre qvq vg!" Most Usenet news reading and posting programs include a rot13 feature. It is used to enclose the text in a sealed wrapper that the reader must choose to open - e.g. for posting things that might offend some readers, or spoilers. A major advantage of rot13 over rot(N) for other N is that it is self-inverse, so the same code can be used for encoding and decoding.

From Jargon File