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Encode or decode text with the classic ROT13 letter-shift cipher.
Uryyb, Jbeyq!ROT13 ("rotate by 13") is a simple substitution cipher that shifts every letter 13 places through the alphabet. Because the alphabet has 26 letters, applying ROT13 twice returns the original text -- making encoding and decoding the exact same operation. It's not real cryptographic security (it's trivially reversible), but it's widely used to hide spoilers, puzzle answers, or mildly sensitive text from casual glances.
Paste any text -- the ROT13 result appears instantly. Paste that result back in to recover the original.
Each letter is shifted 13 positions forward through the alphabet, wrapping around at the end (Z shifts to M). Non-letter characters (numbers, punctuation, spaces) are left unchanged. Case is preserved.
"Hello" becomes "Uryyb". Running ROT13 on "Uryyb" again returns "Hello".
For a configurable-shift version of this same idea, see the Caesar Cipher Tool (ROT13 is just the shift-13 special case).
Take the sentence "The butler did it!" Apply ROT13 letter by letter. T becomes G, h becomes u, and e becomes r, so "The" turns into "Gur". "butler" becomes "ohgyre", "did" becomes "qvq", and "it" becomes "vg". The exclamation mark and the spaces do not change, so the full result is "Gur ohgyre qvq vg!" Paste that result back in and you get the original sentence, because the operation undoes itself. Notice that the case of every letter is preserved: the capital T became a capital G.
New letter position = (old position + 13) mod 26, for A to Z and a to z separately. All other characters are left alone.
A helpful way to see the pattern is to split the alphabet into two halves: A to M and N to Z. ROT13 swaps each letter in the first half with its partner in the second half, so A and N trade places, B and O trade places, and so on. This explains why you can memorize the mapping fairly easily and why there is no separate decode mode. It is also why any letter never maps to itself under this cipher.
Only the 26 basic Latin letters are shifted. Accented letters, letters from other alphabets, digits and symbols pass through unchanged, so a message in another script will not be obscured at all, and an accented character stays readable next to scrambled neighbors. This makes ROT13 a poor fit for anything other than plain English text.
ROT13 is obfuscation, not encryption. Anyone can reverse it in seconds, and no key or secret is involved. Never use it for passwords, personal data, financial details or anything that needs real confidentiality. For genuine protection, use modern, vetted encryption in an appropriate application instead. The realistic uses are lightweight: hiding a spoiler or punchline so that a reader has to make a deliberate choice to reveal it, encoding a puzzle answer, or teaching how substitution ciphers work. If you want to experiment with other shift amounts, the Caesar cipher variant lets you choose the shift, of which ROT13 is the single case with a shift of 13.
No -- it provides zero real security since it's trivially reversible by anyone who recognizes it. It's meant only for casual text obscuring, like hiding a spoiler at a glance.
Because shifting 13 places twice equals shifting 26 places, which is a full trip around the 26-letter alphabet -- landing exactly back where you started.
No -- only letters A-Z (uppercase and lowercase) are shifted; everything else passes through unchanged.
No. Applying ROT13 to already encoded text gives back the original, so the same action encodes and decodes.
No. A shift of 13 always moves a letter to a different one, though numbers, symbols and spaces stay unchanged.
Only letters A to Z are shifted. Other scripts and accented letters pass through unchanged.
Reference: MDN Web Docs