ROT13 Encoder / Decoder
This ROT13 tool shifts every letter 13 places through the alphabet. Because the alphabet has 26 letters, applying the shift twice returns exactly what you started with — which is why the same button both encodes and decodes, and why no separate direction is needed. It is not encryption and offers no security whatsoever; anybody can reverse it in seconds. Its real purpose is hiding text from casual reading: spoilers, puzzle answers, punchlines and answers in forum posts, where the point is that a reader has to choose to reveal it. Any other rotation from 1 to 25 is available too, along with ROT5 for digits.
How it works
ROT13 shifts every letter 13 places through the alphabet. Since the alphabet has 26 letters, applying it twice returns the original — which is why the same button both encodes and decodes.
It is not encryption and offers no security whatsoever. Its actual purpose is to hide text from casual reading: spoilers, puzzle answers and answers in forum posts, where the point is that you have to choose to read it.
Everything runs in your browser — nothing you paste is sent to a server.
ROT13 is its own inverse — run it again to get back what you started with.
Why 13?
There are 26 letters in the alphabet, so a shift of 13 lands exactly halfway. Apply it twice and you have shifted by 26 — a full circle back to where you started. That property is what makes it useful as a convention: nobody needs to remember which direction to go.
It is not encryption
There is no key. Anyone who recognises ROT13 can undo it instantly, and even without recognising it, a frequency analysis breaks it in moments. If you need to protect something, use real encryption — this belongs in the same category as writing an answer upside down.
Other rotations
Any shift from 1 to 25 works, though only 13 is self-inverse. Shift by 3 and you have the cipher Caesar actually used. To reverse a shift of n, apply a shift of 26 − n — the tool tells you which one you need.
Frequently asked questions
How do I decode ROT13?
The same way you encode it. Paste the text and the result appears — applying ROT13 twice returns the original, so one button does both jobs.
Is ROT13 secure?
Not at all. It is a fixed substitution with no key, reversible by anyone in seconds. It hides text from casual reading and nothing more — never use it to protect anything.
What is it actually for?
Concealing spoilers, puzzle answers and punchlines so a reader has to deliberately reveal them. That convention long predates the web and still turns up in forums and newsgroup archives.
What is the difference from a Caesar cipher?
ROT13 is a Caesar cipher with a shift of exactly 13. The shift is chosen so that encoding and decoding are the same operation.
Can I rotate digits too?
Yes. ROT5 shifts the digits 0 to 9 by five places, which is the usual pairing when a string contains numbers as well as letters.
Are punctuation and spacing kept?
Yes. Only letters are rotated; everything else passes through unchanged, so the shape of the text is preserved.
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