Cipher
ROT13 Decoder and Encoder
ROT13 rotates every letter 13 places through the alphabet. Because 13 is exactly half of 26, encoding and decoding are the same operation, so one button does both.
Fcbvyre nurnq
It is famous online for hiding spoilers and punchlines in plain sight. Type anything and the ROT13 version appears instantly, all in your browser.
How the ROT13 works
Each letter moves forward 13 positions, wrapping around the end of the alphabet. A becomes N, N becomes A, and so on. Numbers, spaces and punctuation are untouched.
Since the shift is 13 both ways, running ROT13 on ROT13 output returns the original text. That symmetry is why the same tool encodes and decodes.
Examples
Why ROT13 exists when Caesar already did
ROT13 is a Caesar cipher with the shift fixed at 13, so mechanically there is nothing new here. What makes it a separate thing is what it is for, and that has never been secrecy.
Thirteen is exactly half of twenty-six, which makes ROT13 its own inverse: applying it twice returns the original text. That means one function both encodes and decodes, with no key to pass around and no direction to get wrong. That property, not any strength, is the entire reason it caught on.
It became a convention on Usenet in the early 1980s for hiding punchlines, spoilers and answers to puzzles: text that the reader should have to choose to reveal rather than see by accident. It is a social agreement, not a lock. Everyone can read it, and everyone knows everyone can read it. That is the point.
So the question is not whether ROT13 is secure, because it obviously is not. The question is whether you want a fixed, keyless, self-reversing convention that any reader can undo without instructions. If you do, use ROT13. If you want to choose a shift, use the Caesar page, which also cracks a shift you do not know.
History and origins
ROT13 grew up on early internet forums and Usenet in the 1980s as a light way to hide spoilers, answers and offensive jokes so readers had to opt in to see them.
It was never meant as encryption. It is a social convention, a gentleman's agreement that you will not read the hidden text unless you choose to decode it.
Frequently asked questions
How do I decode ROT13?
Run ROT13 on the encoded text again. Because the shift is half the alphabet, applying it a second time undoes it and reveals the original message.
Is ROT13 secure?
No. It offers zero security and is trivial to reverse. Its whole purpose is to hide text from casual view, such as a spoiler, not to keep secrets.
Learn more
Go deeper on the ideas behind this tool.
Not sure this is the right tool?
If you have a message and you are not certain what it is, the cipher identifier reads the character set and the letter statistics and tells you which scheme it most likely uses, and why. It covers every code and cipher on this site.