🏛️ Caesar Cipher Encoder / Decoder
Shift every letter by a fixed amount, the 2,000-year-old Caesar cipher, encode, decode, or crack an unknown shift by seeing all 25 at once.
🔓 Crack it, try all 25 shifts
Transformed in your browser, nothing you type is uploaded.
How the caesar cipher encoder / decoder works
The Caesar cipher, named after Julius Caesar, replaces each letter with one a fixed number of places later in the alphabet, a shift of 3 turns A into D, B into E, and so on, wrapping Z back to C. Decoding shifts the other way. Because there are only 25 possible shifts, it offers no real security: the built-in "crack it" panel simply shows all 25 decodings so you can pick the readable one.
ROT13 is just the Caesar cipher with a shift of 13, special because applying it twice returns the original, so the same operation encodes and decodes. The Caesar cipher is a teaching classic and a puzzle staple, not a way to protect real data; for that you want the AES file encryption in Privacy & Security.
Frequently asked questions
What is the Caesar cipher?
One of the oldest known ciphers: each letter is shifted a fixed number of positions along the alphabet. With a shift of 3, "HELLO" becomes "KHOOR". Julius Caesar reportedly used it for military messages.
How do I crack a Caesar cipher without the shift?
Try all 25 possible shifts and look for the one that produces readable text, the "crack it" panel here does exactly that automatically. Because there are so few keys, it takes seconds.
Is the Caesar cipher secure?
Not at all, 25 keys is trivially brute-forced, and letter-frequency analysis breaks it even faster. It's valuable for learning and puzzles, not for protecting real information.
What is ROT13?
A Caesar cipher with a shift of 13. Since the alphabet has 26 letters, shifting by 13 twice returns the original, so ROT13 is its own inverse, handy for hiding spoilers or puzzle answers in plain sight.
Does this run locally?
Yes, the shifting is simple arithmetic done in your browser; nothing is uploaded.