Caesar cipher
Shift the alphabet — or try every key at once.
Output
Paste or type above to see the result here.
Your files stay on your device
This tool runs entirely in your browser. What you paste is processed on your device and is never sent to a server, so it is safe to use with tokens, keys and unpublished text.
Example
Example: a clue encoded with shift 3, then cracked without the key
A treasure-hunt clue, “Meet me at the old oak tree at noon”, encoded with Caesar’s own shift of 3. Only the letters move; spaces and punctuation stay put, and capitals stay capitals.
- Encode, shift 3: “Phhw ph dw wkh rog rdn wuhh dw qrrq”.
- Decode, shift 3, turns it back into the clue.
- Without the key, paste the coded text and choose “Try all 25 shifts (crack)”: 25 numbered lines come back, and line 3 is the one that reads as English.
| Line | Text with that shift taken back |
|---|---|
| 1 | Oggv og cv vjg qnf qcm vtgg cv pqqp |
| 2 | Nffu nf bu uif pme pbl usff bu oppo |
| 3 | Meet me at the old oak tree at noon |
| 4 | Ldds ld zs sgd nkc nzj sqdd zs mnnm |
| 13 | Cuuj cu qj jxu ebt eqa jhuu qj deed |
| 23 | Skkz sk gz znk urj ugq zxkk gz tuut |
The key was 3. ROT13 is shift 13 both ways: “Hello, World!” becomes “Uryyb, Jbeyq!”, and encoding that again brings back “Hello, World!”.
How it works
- Type or paste your message and choose Encode, with a shift from 1 to 25 — 3 is Caesar’s own key.
- To read a message, choose Decode with the same shift.
- Don’t know the key? Choose “Try all 25 shifts”: one of the lines will read as plain text — its number is the key.
Frequently asked questions
- How does the Caesar cipher work?
- Every letter moves the same number of places along the alphabet: with a shift of 3, A becomes D, B becomes E, and X wraps round to A. Decoding moves them back.
- How do I translate a Caesar cipher back into English?
- If you know the key, choose Decode with it. If not, choose “Try all 25 shifts (crack)”: one of the 25 lines reads as plain English, and its number is the key.
- What happens to accents, numbers and punctuation?
- They stay as they are: only the 26 letters A to Z are shifted, upper and lower case kept. É, ñ or ß are not moved.
- How do you crack a Caesar cipher?
- There are only 25 possible keys, so try them all: the “all shifts” list shows each one, and the line that makes sense gives the key. That is why the cipher is a puzzle, not real security.
- Is decoding with 3 the same as encoding with 23?
- Yes. Moving every letter 3 places back is the same as moving it 23 places on in a 26-letter alphabet, so Decode 3 and Encode 23 turn “Phhw ph dw wkh rog rdn wuhh dw qrrq” into the same clue.
- What is ROT13?
- A Caesar shift of 13 — half the alphabet — so the same step encodes and decodes. It is used to hide spoilers and puzzle answers.
- Is my text sent anywhere?
- No. It is shifted in your browser.
Made for a specific use
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