Caesar cipher decoder with known shift
Turn Caesar cipher text back into plain text when you know the shift. If you do not know it, use the Caesar brute-force tool.
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Processing and privacy: The result is calculated inside your browser and your data is not sent to any server.
How to use it
- Enter encoded text and shift used to encode.
- The result appears straight away and updates as you edit.
- Copy the result, or copy a link that keeps the same values to share it.
How it is calculated
For each letter with index y from 0 to 25: original = (y - shift) mod 26.
Example
Inputs: Shift used to encode = 3. Result: Decoded text: Hello, World!; Letters processed: 10.
Khoor, Zruog!
Hello, World!
Limits and caveats
- This is a puzzle and teaching cipher that is easy to break, so never use it to protect passwords or sensitive data.
- You need the right shift; a wrong one gives unreadable text.
Questions about this tool
What if I do not know the shift?
Use the Caesar brute-force tool. It shows the text under all 25 shifts and suggests the one that looks most like English.
Is decoding with shift 3 the same as encoding with 23?
Yes, because 3 + 23 = 26, and shifting by 26 returns every letter to itself.
Does it work on Arabic text?
No. It changes Latin letters only and leaves Arabic, digits and symbols untouched.