Caesar cipher
Encrypt with the classic shift cipher, decrypt, or crack an unknown shift.
How to use
- Pick ROT13, the classic shift of 3, or Crack to try every shift.
- Type or paste your text — letters shift, everything else stays.
- In Crack mode, scan the 25 candidate lines for the one that reads as real words.
Frequently asked questions
Why is ROT13 special?
13 is half of 26, so applying ROT13 twice returns the original text — the same button encrypts and decrypts. That convenience made it the internet's spoiler-hider.
Is the Caesar cipher secure?
Not at all — there are only 25 possible keys, and the Crack mode here tries them all instantly. Use it for puzzles and learning, never for real secrets.
What happens to numbers and punctuation?
They pass through unchanged. Only the letters A–Z shift, preserving case.
About this tool
The Caesar cipher is the world's most famous code: shift every letter a fixed number of places down the alphabet, as Julius Caesar reportedly did with a shift of three. Today it is a teaching tool, a puzzle staple and the heart of ROT13 — the shift-13 variant that is its own inverse, long used online to hide spoilers and punchlines. This tool encrypts and decrypts with the classic shift of 3, applies ROT13, and includes a brute-force mode that lists all 25 possible shifts at once — paste any Caesar-encrypted text and simply read down the list until the plaintext jumps out. A neat lesson in why the cipher offers no real security.