How to use this Caesar decoder
- Paste your ciphertext in the box above.
- If you know the shift, move the slider to it and read the decoded text.
- If you don't know the shift, click “Try all 25 shifts” — the table shows every possible decoding, with the most likely one highlighted.
- Copy the result with the Copy button.
What is the Caesar cipher?
The Caesar cipher is one of the oldest ciphers in the world. Each letter of the message is shifted a fixed number of places through the alphabet. With a shift of 3, A becomes D, B becomes E, and HELLO becomes KHOOR. To decode a Caesar cipher, you shift the letters back by the same amount. Julius Caesar used this cipher more than 2,000 years ago to protect military messages — which tells you both how old it is and how simple it is.
ROT13 is the most famous special case: a Caesar cipher with shift 13. Because the alphabet has 26 letters, shifting by 13 twice brings you back to the start, so ROT13 encodes and decodes with the same operation. That is why ROT13 is still used today to hide spoilers, puzzle answers and jokes online.
How to crack a Caesar cipher (brute force)
The Caesar cipher has only 25 possible shifts (a shift of 26 is the same as no shift at all). That means a Caesar cipher solver never has to guess: it simply tries all 25 and checks which one reads as real English. This page does exactly that. It scores each decoding by counting common English words like THE, AND, OF, TO and IS — the decoding with the most real words wins.
For short messages, two or three decodings can look plausible. If the best guess looks wrong, scan the full table of 25 — the right answer is always in there.
Examples
- KHOOR (shift 3) → HELLO
- KHOOR ZRUOG (shift 3) → HELLO WORLD
- GUR CNFFJBEQ VF FHPPRFF (ROT13, shift 13) → THE PASSWORD IS SUCCESS
- WKLQNIXO (shift 3) → THINKFUL
Frequently asked questions
What is a Caesar cipher decoder?
A Caesar cipher decoder reverses a Caesar shift: every letter was moved a fixed number of places through the alphabet. The decoder shifts the letters back to reveal the original message.
How do I decode a Caesar cipher without the shift?
Try all 25 shifts. Only 25 exist, so one of them must be right. This page's brute-force button tests all 25 at once and highlights the one that reads as real English.
What is the Caesar cipher shift for ROT13?
ROT13 is a Caesar cipher with shift 13. Shifting by 13 twice returns the original text, which is why ROT13 is its own inverse.
Is the Caesar cipher real encryption?
No. The Caesar cipher has only 25 possible keys and can be cracked in seconds by brute force. It is a puzzle and a history lesson, not real security.
Related tools
ROT13 Decoder — the shift-13 special case with one-click decoding. Atbash Cipher Decoder — the reversed-alphabet cipher. Vigenère Cipher Decoder — the polyalphabetic upgrade that finally beat simple shift ciphers. Letters to Numbers Converter — turn words into A=1…Z=26 numbers.