About the ROT13 and Caesar Cipher
ROT13 and Caesar Cipher converts text with the classic letter-shifting ciphers. ROT13 moves every letter 13 places along the alphabet, which is why applying it twice gives the original text. The Caesar cipher shifts letters by any number from 1 to 25 and can encode or decode. ROT47 shifts every visible character, letters, digits and symbols, by 47; ROT5 shifts digits only; ROT18 combines ROT13 and ROT5; and Atbash reverses the alphabet. The result updates as you type, and you can copy it in one tap. If you have a coded message and do not know the shift, the tool shows all 25 possible shifts side by side and guesses the likeliest one for English text. These ciphers are for puzzles, games, spoilers and learning: they give no real security, so never use them to protect passwords or private data. The work is done in your browser.
Updated September 2026
How to use the ROT13 and Caesar Cipher
- 1Choose the cipher: ROT13, Caesar, ROT47, ROT5, ROT18 or Atbash.
- 2For a Caesar cipher, choose the shift and whether to encode or decode.
- 3Type or paste your text. The result appears at once.
- 4Copy the result with the Copy button.
- 5If you do not know the shift of a coded message, open Show all 25 shifts and look for the one that reads as words.
How the ciphers work
- ROT13: letters move 13 places; A to N, B to O, and back again with the same step.
- Caesar: letters move by any chosen shift; decode by shifting back.
- ROT47: all printable characters from ! to ~ move 47 places within a range of 94.
- ROT5: only the digits 0 to 9 move 5 places, so 1 becomes 6.
- ROT18: ROT13 for letters and ROT5 for digits at the same time.
- Atbash: the alphabet is mirrored, so A pairs with Z.
Where people use them
ROT13 has long been used on internet forums to hide spoilers, punchlines and puzzle solutions, so that a reader must decide to decode them. Geocaching hints are often written in ROT13, and escape rooms, puzzle hunts and school lessons on codes use Caesar ciphers because they are easy to do by hand.
ROT47 is popular in programming exercises and capture-the-flag games, since it also changes numbers and symbols. Atbash appears in history lessons because it was used in Hebrew texts more than two thousand years ago.
Breaking a shift cipher
A Caesar cipher has only 25 useful keys, so it can be broken by trying each one, and the tool shows all of them in a list. Another way is frequency analysis: in English, the letter e is the most common, so the most common letter in the coded text is likely to stand for e, which points to the shift. The best guess feature applies this idea to longer texts. Very short messages do not have enough letters for a reliable guess.
Only the letters A to Z are shifted. Accented letters, other alphabets, spaces, numbers and punctuation stay as they are, except in ROT47 and ROT5, which handle symbols and digits.
Safety and related tools
None of these ciphers protect information. Anyone can decode them without a key. Use them for fun and learning only. If you want to keep text private, use real encryption with a strong password, and Password Generator can make one. For other encodings, Base64 Encoder Decoder, Binary Translator and Morse Code Translator change text into other representations.
Fancy Text Generator styles text in other ways, and Case Converter changes capitalisation before you encode.
Features
- ROT13, Caesar (1 to 25), ROT47, ROT5, ROT18 and Atbash
- Encode and decode with one tool
- Live result as you type
- Brute-force view of all 25 shifts
- Best-guess shift for English text
- Keeps punctuation, spaces and non-letters as they are
- Runs in your browser
Frequently asked questions
What is ROT13?
ROT13 is a simple cipher that replaces each letter with the letter 13 places after it in the alphabet, wrapping around from Z to A. A becomes N, B becomes O and so on. Because the alphabet has 26 letters, the same step both encodes and decodes: apply ROT13 to a message and then again to get the original back.
What is the Caesar cipher?
It is one of the oldest ciphers, said to have been used by Julius Caesar, and shifts each letter by a fixed number of places. With a shift of 3, A becomes D, B becomes E and HELLO becomes KHOOR. To decode, shift back by the same amount. ROT13 is a Caesar cipher with a shift of 13.
How do I decode a Caesar cipher without the shift?
There are only 25 possible shifts, so you can try them all. Open Show all 25 shifts, and look for the line that makes sense. For English text of some length the tool also guesses the shift by comparing letter frequencies, where e, t and a are the most common letters.
What is the difference between ROT13 and ROT47?
ROT13 only shifts letters, leaving digits and symbols untouched. ROT47 shifts all 94 visible ASCII characters, from the exclamation mark to the tilde, by 47 places, so digits and symbols change too. Like ROT13 it undoes itself when applied twice.
Is ROT13 secure?
No. It is a very weak cipher that anyone can read in seconds, and it is not encryption. It is used for hiding spoilers, puzzle answers and jokes in forums, and for teaching how ciphers work. For real secrecy, use proper encryption with a strong password.
What does Atbash do?
Atbash is an ancient cipher that reverses the alphabet: the first letter becomes the last, the second becomes the second to last and so on, so A becomes Z and M becomes N. Like ROT13 it decodes itself when applied a second time.