Caesar Cipher Decoder & Encoder
Encode or decode a Caesar cipher with any shift from 1 to 25. If you don't know the shift, paste the coded text and read all 25 possible answers at once. The one with the most common English words is marked for you.
Khoor Zruog
Don't know the shift? Try all 25
Each row shifts your text back by a different amount. The row marked “likely” contains the most common English words. Short messages can fool it, so read the rows yourself too.
About Caesar Cipher
A Caesar cipher replaces each letter with the letter a fixed number of places further along the alphabet. With a shift of 3, A becomes D, B becomes E, and X, Y and Z wrap around to A, B and C. "Hello World" becomes "Khoor Zruog". Spaces, digits and punctuation are left alone.
It is named after Julius Caesar. The Roman historian Suetonius wrote that Caesar used a shift of three to protect military messages, and that his nephew Augustus used a shift of one. Caesar's is the first recorded use of this method, though other substitution ciphers existed before it.
How to decode a Caesar cipher
If you know the shift, move each letter back by that many places. With a shift of 3, K → H, h → e, o → l, o → l, r → o, so Khoor becomes Hello. Set the shift box above to the right number and pick Decode.
If you don't know the shift, try them all. There are only 25 possible shifts, so a computer or a patient person can test every one. That is called a brute-force attack. The list above does it for you: only one row should read as normal English. Try it with "Wkh txlfn eurzq ira" and the row for shift 3 reads "The quick brown fox".
Longer messages are easier to crack by hand with letter counts. E is the most common letter in English text, so the most common letter in a long coded message is often an E in disguise. Count the gap between them and you have the shift.
Examples with shift 3
Hello World → Khoor Zruog I love you → L oryh brx attack at dawn → dwwdfn dw gdzq Veni vidi vici → Yhql ylgl ylfl
A shift of one is a famous coincidence: HAL, the computer in 2001: A Space Odyssey, becomes IBM. Arthur C. Clarke said the match was never planned, and that they would have changed the name if they had spotted it.
Caesar cipher, ROT13 and Atbash
ROT13 is a Caesar cipher with a shift of 13. Because 13 is half of 26, shifting twice brings you back to the start, so the same step encodes and decodes. Atbash is a different idea: it mirrors the alphabet (A ↔ Z) instead of shifting it.
None of these hide anything from someone who wants to read them. A Caesar cipher has only 25 keys, so it is a puzzle and a teaching tool, not a way to protect secrets. For that, use modern encryption.
Questions people ask
How does the Caesar cipher work?▼
Each letter moves a fixed number of places along the alphabet, wrapping from Z back to A. To decode, move each letter back by the same number.
How do I decode a Caesar cipher without the key?▼
Try all 25 shifts and look for the one that makes sense. Paste the text above and read the list under the box. The row marked likely contains the most common English words.
Is ROT13 a Caesar cipher?▼
Yes. ROT13 is a Caesar cipher with a shift of 13. It decodes itself, because two shifts of 13 add up to the full 26 letters.
Why is it called a Caesar cipher?▼
Because the Roman historian Suetonius wrote that Julius Caesar used it, with a shift of three, for military messages.
How do I make my own Caesar cipher?▼
Pick a number from 1 to 25 as your key. Move every letter of your message forward by that number, and share the number with the person who will decode it. Or type your message above, set the shift, and copy the result.