Caesar Cipher & ROT13
Explore Caesar shifts and ROT13 with case-preserving letter conversion. Learn substitution with worked examples, entirely in your browser.
Conversion workspace
Input, keys and output stay in this page and are cleared on reload.
Examples and how it works
A Caesar cipher shifts letters by a fixed amount. ROT13 uses a shift of 13, so applying it twice restores the original text.
ROT13 · Decode · shift 13
- Input
- Uryyb, Jbeyq!
- Output
- Hello, World!
Caesar · Encode · shift 3
- Input
- XYZ abc 123
- Output
- ABC def 123
Only A–Z and a–z are shifted, preserving case. Numbers, punctuation and Japanese characters stay unchanged. Choose 0–25 and Decode or Encode. This is not suitable for protecting secrets.
Done
Caesar Cipher & ROT13
How to use
- 1
Choose a shift and direction
Use shift 13 for ROT13. For other Caesar shifts, choose 0–25 and Decode or Encode.
- 2
Enter the text
Enter text containing English letters, then press Convert.
- 3
Check the result
Inspect the output. Digits, punctuation and Japanese text stay unchanged.
Features
- ROT13 and shifts from 0 to 25
- Preserves uppercase and lowercase
- Leaves digits, punctuation and Japanese unchanged
Use cases
Learning data representations
Transform original samples to learn data representations.
Details
Input is limited to 1 MiB measured as UTF-8. Input and output are processed in this page, are not uploaded or saved, and disappear on reload.
FAQ
How do I reverse ROT13?
Apply shift 13 again. Two shifts of 13 return each letter to its original position in a 26-letter alphabet.
Are digits or Japanese characters changed?
No. Only A–Z and a–z are shifted. Digits, spaces, punctuation and Japanese characters stay unchanged.
Can the tool detect the shift automatically?
No. Choose shifts from 0 to 25 manually and compare the output with the exercise instructions.
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Did you know?
ROT13 shifts letters by 13 positions. Applying it twice returns the original letters because the alphabet has 26 letters.