Classical Cipher
Encode and decode Caesar, ROT13, Vigenère, Atbash, and more
- Files never leave your device
- Runs in your browser
- Free, no sign-up, no watermark
Shift
Letter frequency
Type some text with letters to see its frequency.
How to use Classical Cipher
Encode and decode text with nine classical ciphers: Caesar, ROT13, ROT47, Atbash, Vigenère, Affine, Rail fence, Playfair and Substitution. It can crack Caesar automatically and charts letter frequency to help break the others, all in your browser.
- 1
Pick a cipher in the Cipher list.
- 2
Choose Encode or Decode and set the Key: shift, keyword, multiplier and offset, rails, or cipher alphabet, depending on the cipher.
- 3
Type or paste text into Input, or click Sample.
- 4
Read the Result, or click Swap to move it into the input and flip the direction.
- 5
For an unknown Caesar message, click Auto-crack or pick a row under Try all 25 shifts.
Frequently asked questions
Is this safe for protecting real secrets?
No. These are historical ciphers that can be broken by hand. Use them for puzzles, teaching and games, not for passwords or private data.
How does Auto-crack work?
It tries all 25 Caesar shifts and ranks the results by how much they look like English, with the best match on top. Very short or non-English messages may be ranked wrongly, so check the list.
Which values of a can I use in the Affine cipher?
Only values that share no factor with 26: 1, 3, 5, 7, 9, 11, 15, 17, 19, 21, 23 and 25. Other values cannot be decoded.
Why does my Playfair message come back with extra letters?
Playfair works on letters only: J becomes I, doubled letters are split with X, and an odd length is padded. Spaces, digits and punctuation are dropped, so the decoded text keeps those changes.
How do I break a substitution cipher?
Compare the Letter frequency chart with typical English: the most common cipher letter often stands for E, then T, A, O. Edit the Cipher alphabet until the result reads correctly.
What happens to spaces, digits and punctuation?
Most ciphers leave them unchanged and keep letter case. ROT47 also rotates digits and symbols, Rail fence rearranges every character, and Playfair removes them.