Cipher Encoder Decoder | Encode and crack classic ciphers

Encode and decode Caesar, ROT13, ROT47, Atbash, Vigenere, A1Z26 and Bacon ciphers. Includes a brute force table showing all 25 Caesar shifts at once so you can crack a message without the key.


Letters only. Used by the Vigenere cipher.
Clear

What each cipher does

All of these are classical ciphers. They are good for puzzles, games and teaching, and none of them is secure against a computer.

  • Caesar shift. Moves every letter a fixed number of places along the alphabet. A shift of 3 turns A into D. Named after Julius Caesar, who used it for military messages.
  • ROT13. A Caesar shift of exactly 13. Because the alphabet has 26 letters, applying it twice returns the original, which is why it became the standard way to hide spoilers online.
  • ROT47. Like ROT13 but covering all visible ASCII characters, so digits and punctuation are scrambled too. Also its own inverse.
  • Atbash. Mirrors the alphabet: A becomes Z, B becomes Y. It originated in Hebrew scribal tradition and needs no key at all.
  • Vigenere. Uses a keyword to apply a different Caesar shift to each letter in turn. It resisted codebreaking for three centuries and was nicknamed the indecipherable cipher.
  • A1Z26. Simply numbers the alphabet: A is 1, Z is 26. Common in puzzle books and escape rooms.
  • Bacon. Encodes each letter as a five-character group of A and B. Francis Bacon designed it so a message could be hidden in the styling of an innocent text.

How to crack a cipher you cannot read

Start by counting letters. If the letter frequencies look like normal language but the letters are wrong, it is probably a simple substitution such as Caesar or Atbash, and the brute force table on this page will solve a Caesar in seconds. If the frequencies look unusually flat, a keyword cipher such as Vigenere is likely, because it spreads each letter across several different shifts. Groups of five A and B characters point to Bacon, and numbers from 1 to 26 point to A1Z26.

Good to know

  • None of these ciphers is secure. Use them for puzzles and teaching, never for anything you actually need to protect.
  • Spaces and punctuation are left untouched by most of these, which is itself a clue for anyone trying to break the message.
  • A Caesar shift of 13 is exactly ROT13, and a shift of 26 leaves the text unchanged.
  • The processing all happens on our server, so nothing you type is stored or logged.

Frequently asked questions

Try all 25 possible shifts and read the results. This page does that for you automatically: paste the encoded text, run any cipher, and the brute force table shows every shift at once. Scan down until one line reads as ordinary language, and the number next to it is the shift that was used.

It moves every letter a fixed number of positions along the alphabet. With a shift of 3, A becomes D, B becomes E, and Z wraps around to C. Julius Caesar reportedly used a shift of 3 for military correspondence, which is where the name comes from. There are only 25 useful shifts, so it takes seconds to break.

ROT13 is a Caesar shift of 13 and is not meant to be secure. Because 13 is exactly half of 26, applying it twice restores the original text, so the same operation both hides and reveals. That made it the traditional way to obscure spoilers, punchlines and puzzle answers in forums and newsgroups.

It applies a different Caesar shift to each letter, chosen by a repeating keyword. With the keyword KEY, the first letter shifts by K, the second by E, the third by Y, then it repeats. Because the same plaintext letter can encode to different letters, simple frequency analysis fails, which is why it went unbroken for around three hundred years.

Atbash reverses the alphabet, so A maps to Z, B to Y, C to X and so on. It needs no key, and because the mapping is symmetrical, running it twice returns the original text. It comes from Hebrew scribal practice and appears in ancient texts.

No, and none has been for a very long time. Every cipher on this page can be broken by hand with patience, and instantly by a computer. They are excellent for puzzles, escape rooms, treasure hunts and teaching how encryption works, but real security needs modern cryptography.

It is the alphabet written as numbers: A is 1, B is 2, through to Z which is 26. Encoded messages look like sequences such as 8-5-12-12-15 for HELLO. It appears constantly in puzzle books and escape rooms because it needs no explanation once you spot the pattern.

No. The text is sent to our server over an encrypted connection, transformed in memory and returned immediately. Nothing is written to a log, a file or a database. Even so, these are puzzle ciphers, so there is no reason to put genuinely sensitive text through them.

What is a cipher encoder and decoder?

A cipher encoder and decoder converts text into and out of classical ciphers such as Caesar, ROT13, Atbash and Vigenere. If you do not know the Caesar shift, this page also shows all 25 shifts at once, so you can read down the list and spot the one that makes sense.