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ROT13 / Caesar cipher

Shift letters through the alphabet by any amount, ROT13 by default.

Input
13
Output
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ROT13 / Caesar cipher
ROT13 replaces every letter with the one thirteen places further along the alphabet: a becomes n, n becomes a. Thirteen is exactly half of twenty-six, which is why the same operation both encodes and decodes — run the text through twice and you are back where you started. That quirk made it the standard way to hide punchlines, spoilers and puzzle answers on Usenet and forums from the 1980s onwards. Move the shift slider anywhere between 1 and 25 and you get the general Caesar cipher, the one Julius Caesar reportedly used with a shift of three.
Pick encrypt or decrypt: at ROT13 the direction makes no difference, at every other shift it does. Only the twenty-six unaccented Latin letters rotate, and their case is preserved — spaces, punctuation, accented letters, emoji and non-Latin scripts pass through untouched, exactly as the cipher is defined. Switch on "Shift digits too" and 0–9 rotate by five as well; ROT13 plus ROT5 is known as ROT18 and is likewise its own inverse. Faced with a message and no key, turn on "Show all 25 shifts" and the tool prints every candidate decoding labelled with its shift, so the readable line names its own key.
A Caesar cipher is a classic, not a security measure. Twenty-five keys fall in less time than it takes to read this sentence, and the brute-force preview built into this page proves the point. Use it for puzzles, CTF warm-ups, teaching and spoilers. For text that genuinely needs protecting, use the encrypt text tool, which derives an AES-256-GCM key from your password.
Everything runs in your browser, so nothing is uploaded and the page works offline. Copy the result, download it as .txt, or move it back to the input and chain another step.
FAQ
Why does ROT13 encode and decode with the same button?
Thirteen is half of twenty-six, so shifting twice returns every letter to where it started. At any other shift you have to pick decrypt and use the same number the text was encoded with.
Can I use a shift other than 13?
Yes. The slider covers 1 to 25, which is the full Caesar cipher. Shift 3 is the historical one; shift 47 or 0 would be meaningless, so the range stops where the alphabet does.
What happens to accented letters, digits and emoji?
They pass through unchanged. The cipher is defined over the 26 letters A–Z only, so "č", "ß" and "🫐" come out exactly as they went in. Digits move only if you enable ROT5.
Is ROT13 secure?
No, and it was never meant to be. There are only 25 possible keys and this tool can show all of them at once. Treat it as obfuscation for fun, and use password-based encryption for anything that matters.
Is my text uploaded anywhere?
No. The tool runs entirely in your browser and your text never leaves your device.