🏛️ 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.