Codes / Classical ciphers
Caesar Cipher Encoder and Decoder
Encrypt and decrypt text with the Caesar cipher at any shift, see the shifted alphabet, and crack an unknown shift by trying all 25 with the likeliest English shown first.
Caesar Cipher Encoder and Decoder: The Caesar cipher replaces each letter with the one a fixed number of places further along the alphabet, wrapping from Z back to A; Julius Caesar is said to have used a shift of 3. Capitals and small letters keep their case, and digits, spaces, and punctuation are left alone. Trying all shifts is easy because there are only 25; the tool ranks them by how closely their letter frequencies match English. Runs 100% locally in your browser with zero server file uploads.
- Category
- Text tools
- Runs
- In your browser
- Cost
- Free · no sign-up
- Availability
- Ready to use
Runs entirely in your browser
Breaking a shift by hand
In English the most common letter is E, so the most common letter of a Caesar ciphertext is probably E in disguise: if it is H, the shift is 3. Short words help too, since a lone letter is usually A or I.
For a cipher that resists this, try the Vigenère cipher; for real secrets, encrypt text with a password instead.
In classrooms
A paper Caesar wheel, two discs with the alphabet around the edge, makes the shift visible: turn the inner disc by the shift and read across. The shifted alphabet above does the same.
How to use it
- Type or paste your text, and choose Encrypt or Decrypt.
- Set the shift; the alphabet below shows where each letter goes.
- To crack a message, tick Try all 25 shifts and pick the one that reads as words.
Privacy & limitations
Your text stays in your browser.
Related tools
Frequently asked questions
Is the Caesar cipher secure?
No: with only 25 possible shifts, anyone can try them all in seconds. It is a puzzle and a teaching example, not protection for real secrets.
How do I decrypt without knowing the shift?
Tick Try all 25 shifts: the decryption that reads as normal words is the answer, usually the first one listed for English text.
What is the difference from ROT13?
ROT13 is the Caesar cipher with a shift of 13; because 13 is half of 26, the same operation both encrypts and decrypts.
Free tool · runs in your browser · no account required