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Caesar Cipher Encoder & Decoder

The classic Caesar cipher replaces each English letter with the letter three positions further along the alphabet, wrapping Z back to A. Decryption moves three positions back. This tool uses that fixed shift; use our Shift Cipher tool to choose another key.

Classic Caesar cipher: fixed shift of 3.

0 / 50,000 characters

Letter mapping · Shift 3

Input alphabetABCDEFGHIJKLMNOPQRSTUVWXYZ
Output alphabetDEFGHIJKLMNOPQRSTUVWXYZABC

Your text is processed in this browser. It is not uploaded or saved by this tool. No account required.

Decode without knowing the shift

Try all 26 possible shifts on your input, including 0 (unchanged). Read the candidates to find meaningful text; this tool does not automatically identify the correct answer.

How to encrypt or decrypt a Caesar cipher

1

Enter your text

Paste plaintext to encrypt, or a Caesar message to decrypt.

2

Choose an operation

Encrypt moves letters forward by 3; decrypt moves them back by 3. The result updates as you type.

3

Use the result

Copy or download the result. Reverse it to verify that the original text returns.

Caesar cipher example: HELLO → KHOOR

With a shift of 3, H becomes K, E becomes H and L becomes O. HELLO, WORLD! becomes KHOOR, ZRUOG!; decrypting restores HELLO, WORLD!. X, Y and Z wrap to A, B and C.

Number A–Z from 0 to 25. Encryption is E(x) = (x + 3) mod 26; decryption is D(x) = (x − 3 + 26) mod 26.

Supported text and limits

  • Only A–Z and a–z are shifted; uppercase and lowercase are preserved. Digits, punctuation, spaces, accented letters, Chinese, Cyrillic and emoji stay unchanged.
  • Up to 50,000 characters per input. Use this classical cipher for learning and puzzles; it is easily broken and should not protect sensitive information.

Frequently asked questions

What is a Caesar cipher?

A Caesar cipher is a substitution cipher that moves letters a fixed distance along the alphabet. The historical Caesar key is 3, which this page uses. The term also commonly refers to other fixed shifts.

How do I decrypt a Caesar cipher with shift 3?

Select Decrypt and paste the ciphertext. Each English letter moves three positions back: KHOOR becomes HELLO, and A wraps back to X.

How is Caesar cipher different from shift cipher?

They use the same rotation method. This Caesar page fixes the key at 3; our Shift Cipher page lets you choose any whole-number key, including 13 for ROT13.

Can I decode a Caesar cipher without the key?

Yes. Open the candidate section to see all 26 possible shifts and look for readable text. There are only 25 nonzero shifts for the English alphabet.

Does the tool change Chinese text or punctuation?

No. Only ASCII English letters A–Z and a–z rotate. Letter case is preserved; other characters, including accented letters, remain unchanged.

Is Caesar cipher secure, and is my text uploaded?

Caesar cipher is easy to break and is useful for learning and puzzles, not protecting secrets. This tool processes your text locally in the browser without uploading or saving it.

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