Cipher
Caesar Cipher Decoder and Encoder
The Caesar cipher shifts every letter a fixed number of places along the alphabet. Choose a shift, type your message, and read the result live. Set the shift to decode a message someone sent you.
Result appears here
It is the friendliest cipher to learn and the classic first puzzle in cryptography. All the work happens in your browser.
How the Caesar Cipher works
Pick a shift number from 1 to 25. Each letter moves that many places forward through the alphabet, wrapping around from Z back to A. A shift of 3 turns A into D and Z into C.
To decode, apply the same shift in reverse (or set the tool to decode). Non-letters like spaces and punctuation are left untouched.
Examples
History and origins
Named after Julius Caesar, who according to the historian Suetonius shifted letters by three to protect his military correspondence. It is one of the oldest recorded ciphers.
By modern standards it offers no real security, since there are only 25 possible shifts to try. That very weakness makes it perfect for teaching how substitution ciphers work and how they are broken.
Frequently asked questions
What shift should I use to decode a Caesar cipher?
If you do not know the shift, try each value from 1 to 25 and watch for readable text. With only 25 options this brute-force check takes seconds.
Is ROT13 a Caesar cipher?
Yes. ROT13 is simply a Caesar cipher with a shift of 13. Because 13 is half of 26, applying it twice returns the original text.
Why is the Caesar cipher considered insecure?
There are only 25 possible keys, so anyone can try them all in moments. It is a teaching cipher, not a way to protect real secrets.
Learn more
Go deeper on the ideas behind this tool.