Cipher Tools: Caesar, ROT13, Vigenère and More
Encode and decode Caesar, ROT13, Atbash, A1Z26, Vigenère and NATO. Runs in your browser.
About this cipher tools: caesar, rot13, vigenère and more
These cipher tools encode and decode the classic hand ciphers: Caesar, ROT13, ROT47, Atbash, A1Z26 and Vigenère, plus the NATO phonetic alphabet. They are made for puzzle hunters, escape-room builders, teachers and anyone who found a strange message and wants to read it.
Lost the key? For Caesar, decode mode lists all 25 shifts and marks the one that reads most like English. For Vigenère, Guess the key estimates the key length and the key itself from the letter statistics of your message.
One thing to be clear about: none of these ciphers protect anything. They are fun and good for learning, but a computer breaks them instantly. For real secrets, use AES encryption.
Features
Seven ciphers in one box
Switch between Caesar, ROT13, ROT47, Atbash, A1Z26, Vigenère and NATO without retyping.
Ranked Caesar brute force
Decode mode shows every shift, scored by a chi-squared test against English letter frequencies. The likely answer is marked. Click a row to set that shift.
Vigenère key guessing
Finds the probable key length with the index of coincidence, then solves each letter of the key by frequency analysis. You get up to three candidate keys with a preview of the decoded text.
Key stream view
Under a Vigenère result, the key letters line up with your message so you can see which shift each letter got. Spaces and punctuation don't use up key letters.
NATO alphabet both ways
Spell text as Alfa Bravo Charlie, with digits as Zero to Nine or the radio forms Tree, Fower and Niner. Paste code words and they turn back into text, even with Alpha or Juliet spellings.
Case and punctuation kept
Letters keep their case and everything else passes through, so a decoded sentence still has its spaces, commas and numbers. ROT47 is the exception, because it rotates punctuation and digits on purpose.
How to use the cipher tools: caesar, rot13, vigenère and more
- 1Pick a cipher and choose Encode or Decode.
- 2Type your text and set the shift or key.
- 3Copy the result. To crack a Caesar shift, read the brute-force table.
When to use it
Escape rooms and puzzle hunts
Try each cipher on the clue in turn. If Caesar's brute force shows nothing readable, try Atbash, then A1Z26 if the clue is numbers. Dots and dashes belong to the Morse code translator instead.
Hiding spoilers
ROT13 has hidden punchlines and spoilers on forums for decades. Readers who want the answer run it through ROT13 again.
Teaching cryptography
Encrypt a paragraph with Vigenère, then let the class crack it with Guess the key. It shows in five minutes why frequency analysis beat these ciphers. Compare with a modern hash to show how far things have come.
Reading codes over the phone
Booking references and serial numbers are easy to mishear. Paste the code, choose NATO, and read out Bravo Alfa Two Four Niner Zero.
How does the Caesar cipher work?
Each letter moves a fixed number of places along the alphabet, wrapping from Z back to A. With a shift of 3, A becomes D, B becomes E and Z becomes C. HELLO becomes KHOOR. To decode, shift back by the same number.
The Roman historian Suetonius wrote that Julius Caesar used a shift of three in private letters. With only 25 useful shifts, anyone can try them all by hand in a few minutes. A computer does it in under a millisecond.
How do you crack a Caesar cipher without the key?
Try every shift and look for English. This tool does that and ranks the results. For each shift it counts the letters in the result and compares them with how often each letter appears in typical English text, where E is about 12.7%, T about 9.1% and Z under 0.1%. The shift whose letter mix is closest wins.
Short messages can fool the score. With fewer than about 20 letters, read the top few rows yourself rather than trusting the marked one.
How does the Vigenère cipher work, and how is it broken?
Vigenère uses a keyword. Each letter of the key sets a Caesar shift for one letter of the message: A shifts by 0, B by 1, up to Z by 25. With the key LEMON, the first letter shifts by 11, the second by 4, and so on, repeating the key. The same plain letter can come out differently each time, which beat simple frequency counts for about three centuries.
It falls to statistics once you have enough text. If the key is five letters long, every fifth letter used the same shift. Those letters, taken together, have the uneven letter mix of English. The index of coincidence measures that: about 0.066 for English and about 0.038 for random letters. Once the length is known, each column is a plain Caesar shift and is solved like one.
- Under 60 letters: guesses are often wrong.
- 100 to 200 letters: short keys of up to 5 or 6 letters are usually found.
- Longer keys need proportionally more text.
What are ROT13, ROT47, Atbash and A1Z26?
ROT13 is a Caesar shift of 13. Since the alphabet has 26 letters, doing it twice gives the original back. ROT47 does the same trick over the 94 printable ASCII characters from ! to ~, so digits and symbols change too. Atbash reverses the alphabet, A with Z and B with Y, and comes from ancient Hebrew writing. A1Z26 replaces each letter with its number in the alphabet, so CAT is 3-1-20.
Why use Mavros
| Mavros | Typical upload sites | |
|---|---|---|
| Ciphers on one page | Seven, same input box | One cipher per page |
| Caesar brute force | All shifts, ranked by English score | Unranked list |
| Vigenère key finding | Key length and key, with previews | Rare on simple sites |
| Key stream view | Shown under the result | Rare |
| NATO decoding | Code words back to text | Encode only |
| Privacy | Nothing leaves your browser | Varies |
Tips
- Look at the ciphertext first. Only letters changed? Try Caesar, Atbash or Vigenère. Numbers 1 to 26? A1Z26. Symbols changed too? ROT47.
- Vigenère keys with repeated letters or real words are easier to crack. A random 12-letter key holds out much longer, but still not against a computer.
- To make a message look like gibberish and also be secure, use AES. To make a strong key for it, the password generator is a good start.
Questions
How do I decode a Caesar cipher?
Choose Caesar and Decode, then paste the text. If you know the shift, set it on the slider. If you don't, the table below lists all 25 shifts and marks the one that reads most like English.
Is the Caesar cipher secure?
No. It has only 25 possible keys, so trying them all takes seconds. None of the ciphers on this page are secure. Use AES or another modern cipher for anything private.
How do I decode ROT13?
Run it through ROT13 again. A shift of 13 applied twice moves each letter 26 places, back where it started, so encoding and decoding are the same step.
What is the difference between ROT13 and ROT47?
ROT13 only rotates the 26 letters and leaves digits and punctuation alone. ROT47 rotates all 94 printable ASCII characters, so numbers and symbols are scrambled too.
How does the Vigenère key guesser work?
It tries key lengths from 1 to 16, measuring how English-like each set of every nth letter looks with the index of coincidence. For the best lengths, it solves each key letter by matching English letter frequencies.
What is the A1Z26 cipher?
Each letter becomes its position in the alphabet: A=1, B=2, through Z=26. Letters in a word are joined with dashes and words are split by spaces, so HI THERE is 8-9 20-8-5-18-5.
Why is it spelled Alfa and Juliett in the NATO alphabet?
Those are the official ICAO spellings. Alfa uses an f because ph is not read as an f sound in every language, and the double t in Juliett tells French speakers the final t is not silent.
Is my message sent anywhere?
No. Every cipher runs in your browser and nothing is uploaded. Short messages are kept in the page address, so the link shares your text.