Caesar cipher
The Caesar cipher shifts every letter by the same fixed amount, classically three positions. It is the simplest special case of the Vigenère cipher: a one-letter key. Choose a shift from 0 to 25 to encrypt or decrypt.
Break without the shift
Paste Caesar ciphertext with an unknown shift and the solver tries all 26, ranking each by how much the result looks like English.
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About the Caesar cipher
The historian Suetonius records that Julius Caesar protected private letters by replacing each letter with the one three places further down the alphabet, so A became D and X wrapped around to A. Any fixed shift from 1 to 25 works the same way; the shift value is the whole key. ROT13, the shift of 13 used to hide spoilers online, is a Caesar cipher that undoes itself when applied twice.
With only 25 possible keys, the cipher offers no real security: trying every shift and picking the one that reads as language takes moments by hand and microseconds in a browser, which is exactly what the solver above does. It survives today as a teaching cipher and as the building block of the Vigenère family, where a different Caesar shift is applied at each key position.