Caesar Cipher Encoder & Decoder
Drag the shift from 0 to 25 and see the encoded and decoded text update at once, with case and punctuation left alone. A ROT13 preset is one click away. It runs in your browser.
This Caesar cipher tool rotates each letter by a fixed number of places and shows the result live as you move the slider. It doubles as a ROT13 encoder — set the shift to 13, the value that’s its own inverse — and as a Caesar cipher decoder, since the decoded pane always shows what the same shift would undo. Digits, spaces and punctuation pass through untouched, so only the letters change. Nothing is sent anywhere; the shift cipher runs entirely in your browser.
How it works
- 1
Enter your text
Type or paste text into the left box. To decrypt, paste the ciphertext there instead.
- 2
Set the shift
Drag the slider from 0 to 25, or hit the ROT13 preset for a shift of 13.
- 3
Read the result
The encoded pane shows the shifted text and the decoded pane shows the reverse. Copy whichever you need.
Instant & 100% private — nothing is uploaded
Everything runs locally in your browser. Your code, text and files are processed on your own device and are never sent to a server — so there are no upload waits, no size limits from us, and nothing is ever stored or logged.
Frequently asked questions
- How do I decode a Caesar cipher if I don’t know the shift?
- Paste the ciphertext and drag the slider through the 25 shifts, watching the decoded pane. Because every option is shown live, the readable one tells you the shift that was used.
- What is ROT13?
- ROT13 is a Caesar cipher with a shift of 13. Since the alphabet has 26 letters, applying it twice returns the original text, so the same button both encodes and decodes.
- Does the shift cipher change numbers and punctuation?
- No. Only A–Z and a–z are rotated. Digits, spaces, symbols and line breaks stay exactly as you typed them, and letter case is preserved.
- Is a Caesar cipher secure?
- Not at all — with only 25 possible shifts it’s trivial to break, which is why this is a learning and puzzle tool rather than real encryption.
- Can I use it for ciphers like ROT5 or ROT18?
- The slider covers any letter shift from 0 to 25, so ROT5-style letter rotations work. This tool only rotates letters, not digits.
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