Caesar Cipher Text
Shift every letter by a chosen amount to encode or decode a message.
Caesar Cipher is a free online tool that shift every letter by a chosen amount to encode or decode a message. It runs entirely in your web browser using plain JavaScript, so files are processed on your own device and never uploaded to a server. There is no sign-up, no file size limit imposed by the site, no watermark and no paid tier.
- Price
- Free — no account, no quota, no watermark
- Category
- Text
- Where it runs
- In your browser, on your device
- Files uploaded
- None
- Technology
- plain JavaScript
- Settings
- 1
- Works offline
- Yes, after the first visit
About Caesar Cipher
Named for Julius Caesar, who according to Suetonius used a shift of three for military correspondence. Each letter moves a fixed number of places through the alphabet. With only 25 possible non-trivial keys it can be broken by trying all of them, and even without doing so, letter-frequency analysis — a technique described by al-Kindi in the 9th century — recovers the shift from a paragraph of text almost instantly.
How to use it
- Paste the text you want to run through caesar cipher.
- Set shift.
The one setting
| Setting | What it does | Default |
|---|---|---|
| Shift | Range -25–25. | 3 |
Under the hood
| Runs on | plain JavaScript — runs the whole thing |
| Controls | Shift |
Questions
How do I break one without the key?
Try all 25 shifts and read them; one will be English. For longer text, count letter frequencies — the most common letter is very likely a shifted E, which gives you the key directly.
What shift does ROT13 use?
13, exactly half of 26, which is what makes it its own inverse. Any other shift needs the opposite shift to decode.
What are the limits on shift?
It accepts -25 to 25, starting at 3.