ROT13 Encoder and Decoder

Every variant undoes itself, so there is no separate decode switch.

1. Type or paste your text into the Input box.
2. Choose a Variant: ROT13 (letters) is the default, ROT5 (digits), ROT18 (letters + digits) and ROT47 (all printable ASCII) are the others.
3. Read the rotated text in the output box. It updates as you type.
4. To decode, paste the rotated text back in with the same variant, or press Use as input to send the output back round.
5. Press Copy or Download .txt when you are done.

The rotation runs in your browser, and nothing is uploaded. Characters a variant does not cover are left as they were, and line breaks and spacing are untouched, so a rotated paragraph keeps its layout and can be pasted straight back into a forum post or document.

ROT13 moves each letter 13 places along the alphabet and wraps from Z to A, keeping case. The alphabet has 26 letters, so doing it twice returns the start. ROT5 does the same for digits, adding five to each, so 0 swaps with 5 and 1 with 6. ROT18 is ROT13 for letters and ROT5 for digits together. ROT47 works on the 94 printable ASCII characters from ! (code 33) to ~ (code 126), adding 47 and wrapping, which also changes punctuation and digits. Spaces are never touched, and letters outside plain English, such as é, pass through unchanged.

ROT13 became a habit on Usenet in the 1980s as a courtesy: spoilers, joke punchlines and puzzle answers were rotated so that nobody read them by accident, and anyone who wanted to could reverse it in a second. Geocaching hint text still follows that convention, and some text editors and mail programs include a ROT13 command for the same reason. It is not security. There is no key, and every rotation is public knowledge, so never use it for passwords or private data.

Worked example: The butler did it becomes Gur ohgyre qvq vg. Letters pair up neatly, A with N, B with O, and so on to M with Z, which is why the same pass reverses itself.

ROT13 is a Caesar cipher with the shift fixed at 13, so the Caesar cipher tool can reproduce it and also try other shifts. If you want text that looks different instead of scrambled, the upside down text generator and the reverse text generator change its appearance while staying readable by eye.

• Nothing seems to change. Rotating twice returns the original. If the output matches your input, you may have fed it the result of an earlier pass.
• Digits stayed the same. ROT13 only touches letters. Choose ROT18 to rotate digits as well, or ROT5 for digits alone.
• Combining passes. ROT13 followed by ROT5 gives the same result as ROT18 in one go, because letters and digits are separate sets, but this does not hold for ROT47, which touches both.
• Mixed variants. Text rotated with ROT47 must be reversed with ROT47. Using ROT13 on it gives a different mess.
• Awkward characters. ROT47 output can contain quotes, backticks and backslashes, which may need escaping if you paste it into code or Markdown.
• Letters with accents. Only plain A to Z letters rotate. A word such as café becomes pnsé under ROT13, so the accented letter stays visible and gives a clue.

It also helps to know what the tool does not do. There is no way to choose a different number of places; for that, use a Caesar shift. There is no file input, and nothing is stored between visits, so copy any result you want to keep before closing the page.