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ROT13 Encoder / Decoder

Type or paste text and see the ROT13 version instantly. ROT13 is its own inverse, so the same box encodes and decodes. Switch to ROT47, ROT5, ROT18 or a custom Caesar shift, and let the tool find the shift of an unknown Caesar message.

Input text0

ROT13 result0

Substitution table

How to use the ROT13 Encoder / Decoder

Pick a cipher: ROT13 (default), ROT47, ROT5, ROT18 or Caesar shift.
Type or paste your text into the input box. The result updates as you type.
To decode ROT13, ROT47, ROT5 or ROT18, just paste the encoded text: these ciphers undo themselves.
For a Caesar cipher, set the shift and choose Encode or Decode. If you do not know the shift, press Find shift to see all 25 options with the best English match first.
Copy or download the result, or press Swap to move it back to the input.

ROT13 alphabet

Plain	A	B	C	D	E	F	G	H	I	J	K	L	M
ROT13	N	O	P	Q	R	S	T	U	V	W	X	Y	Z

The second half of the alphabet maps back to the first (N→A … Z→M). Example: Hello, World! becomes Uryyb, Jbeyq!, and applying ROT13 to Uryyb, Jbeyq! gives Hello, World! again.

The formulas

Caesar / ROTn for letters: encoded = (letter position + n) mod 26, with A = 0. Decoding uses (position − n) mod 26. ROT13 is n = 13, so encoding and decoding are the same.
ROT5 for digits: encoded digit = (digit + 5) mod 10.
ROT47: for any character with ASCII code c between 33 and 126, encoded = 33 + ((c − 33 + 47) mod 94). Spaces and characters outside that range stay the same.

Where ROT13 is used

ROT13 became popular on Usenet in the 1980s to hide spoilers, punchlines and puzzle answers so readers had to choose to reveal them. It is still used in geocaching hints, forums, programming exercises and puzzle hunts. The Caesar cipher is much older: the Roman historian Suetonius wrote that Julius Caesar used a shift of three letters in private letters.

Frequently asked questions

What is ROT13?

ROT13 (rotate by 13 places) is a simple letter substitution cipher that replaces each letter with the letter 13 positions after it in the alphabet, wrapping around from Z to A. So A becomes N, B becomes O and N becomes A. Numbers and punctuation are not changed.

How do I decode ROT13?

Apply ROT13 again. Because the English alphabet has 26 letters, shifting by 13 twice brings every letter back to where it started. Paste the encoded text into the box and the decoded text appears in the result.

What is the difference between ROT13 and ROT47?

ROT13 only changes the 26 letters. ROT47 rotates all 94 printable ASCII characters from ! to ~ by 47 places, so digits and symbols are scrambled too. Both are their own inverse.

Is ROT13 secure encryption?

No. ROT13 and the Caesar cipher hide text from a casual glance, such as spoilers or puzzle answers, but anyone can reverse them in seconds. Never use them to protect passwords or private data.

How does the Caesar shift finder work?

It decodes the text with all 25 possible shifts and compares the letter frequencies of each result with typical English letter frequencies using a chi-squared score. The shift whose letters look most like English is listed first. It works best with a sentence or more of text.

Does ROT13 work with accented letters or other alphabets?

Classic ROT13 is defined only for the basic Latin letters A to Z. Accented letters, other alphabets, emoji, digits and punctuation pass through unchanged (except digits in ROT5 and ROT18).

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