ROT13 and Simple Ciphers
Choose a classic letter cipher, type your message and read the result straight away. Most of these undo themselves when you run them twice.
Worked examples
ROT13
Hello, World!
Uryyb, Jbeyq!
Run the result through again to get the original back.
Atbash
Hello, World
Svool, Dliow
A and Z swap, B and Y swap, and so on.
Affine, a = 5 and b = 8
AFFINE CIPHER
IHHWVC SWFRCP
Each letter number x becomes 5x + 8, wrapped at 26.
About ROT13 and Simple Ciphers
ROT13 is the best known of the simple letter ciphers. It moves every letter 13 places along the alphabet, and because the alphabet has 26 letters, doing it twice returns the original, so the same step encodes and decodes. It has long been used to hide spoilers, puzzle answers and punchlines. This page offers ROT13 and the other classic ciphers that work the same simple way.
ROT5 does the same for digits, ROT18 handles letters and digits together, and ROT47 rotates all the visible characters from ! to ~. Atbash swaps each letter with its mirror, so A becomes Z. A1Z26 turns letters into their place in the alphabet. The affine cipher multiplies and shifts. All of them keep the case of letters and leave other characters alone, and none gives real protection, so treat them as puzzles and not as a way to hide anything important.
How to use ROT13 and Simple Ciphers
- Choose the cipher from the menu.
- Type or paste your message in the box. The result appears straight away.
- For A1Z26 and affine, choose encode or decode, and set the separator, or the multiplier and shift.
- Copy the result, or use it as the new input to check that it decodes.
Common uses
- Hiding a spoiler or a puzzle answer so it is not read by accident
- Solving or setting a cipher puzzle for a treasure hunt or a lesson
- Checking a message you were given in ROT13 or Atbash
- Teaching how substitution ciphers work
Frequently asked questions
How do I decode ROT13?
Put the encoded text in and read the result. ROT13, ROT5, ROT18, ROT47 and Atbash undo themselves, so the same step both encodes and decodes.
Which multipliers can I use in the affine cipher?
The multiplier must have no factor in common with 26, which leaves 1, 3, 5, 7, 9, 11, 15, 17, 19, 21, 23 and 25. Otherwise two letters would encode to the same letter and the message could not be decoded.
How does A1Z26 show spaces between words?
Letters in a word are joined by the separator you choose, and words are separated by a slash, so HELLO WORLD becomes 8-5-12-12-15 / 23-15-18-12-4. Decoding reads the same layout.
Is this a good way to hide a message?
No. These ciphers can be broken in seconds. They are for puzzles and light hiding of text from a casual glance, not for anything that must stay confidential.