How to use the Caesar cipher converter
Enter text in Input text, choose Encrypt or Decrypt, and set Shift. The Caesar cipher converter changes ASCII letters in the output while keeping their case. Spaces, digits, punctuation, line breaks, and other characters keep their original positions.
How to encrypt or decrypt text
- Type or paste text into
Input text, or click Upload to select a.txtortext/plainfile. - Under Conversion mode, choose Encrypt to move letters forward or Decrypt to move them backward.
- Set Shift with the slider or enter a number in Shift value. The two Shift controls stay in sync, and the result updates when you edit the text or options.
- Read the changed text in
Converted output. Click Copy to copy it or Download .txt to savecaesar-cipher-output.txt.
What Shift and ROT13 preset change
Shift sets the number of alphabet positions for each ASCII letter. The alphabet wraps at its ends, so Encrypt with Shift value 3 changes X to A. Decrypt uses the same value in the reverse direction.
Input: Hello, World!
Mode: Encrypt
Shift value: 3
Output: Khoor, Zruog!ROT13 preset sets Shift to 13. It keeps uppercase letters uppercase and lowercase letters lowercase. Applying ROT13 twice returns the original ASCII letters.
What the converter leaves unchanged
The converter changes A-Z and a-z only. Accented letters, other Unicode letters, digits, spaces, line breaks, and punctuation pass through unchanged. A blank or non-numeric Shift value uses 3. Numeric values outside the 1 to 25 range are clamped to that range.
The conversion runs in browser-side JavaScript. The page code contains no fetch, XMLHttpRequest, sendBeacon, or form post that sends the entered text. Copy and Download .txt stay disabled while the output is empty.
What you can check with a Caesar cipher
- Enter a phrase, choose Encrypt, and copy the shifted text for a short alphabet-shift exercise.
- Use Decrypt with the same Shift value to reverse text that was encrypted with that value.
- Check alphabet wraparound with
xyzand Shift value 3. The output isabc.
When another text conversion tool fits better
Use Text Conversion Tools for a different text representation. Choose the Vigenere Cipher Converter when the conversion should use a keyword. Choose the Base64 Encoder / Decoder for Base64 encoding or decoding, or the Unicode Converter for \uXXXX escapes and hidden-character inspection.
Frequently asked questions
How do I decrypt a Caesar cipher?
Choose Decrypt and enter the same Shift value used for encryption. The converter moves each ASCII letter backward and keeps its case and surrounding characters.
What is the ROT13 preset?
ROT13 is a Caesar shift of 13, and ROT13 preset sets Shift to 13. Applying that same setting twice restores the original ASCII letters.
Does a Caesar cipher change numbers or punctuation?
Numbers, punctuation, spaces, line breaks, and letters outside ASCII A-Z and a-z remain unchanged.
Can I use a Caesar cipher for sensitive text?
A Caesar cipher has 25 selectable shifts and uses one fixed letter offset. That makes it suited to puzzles and demonstrations, rather than protecting sensitive information.
Does my text stay in the browser?
Yes. The page converts the entered string in browser-side JavaScript, and its page code has no request that sends the entered text to a server.