Caesar Cipher & ROT13

Encrypt or decrypt text with a Caesar shift (1–25), ROT13 or ROT47. Don't know the shift? The cracker tries all 25 and ranks them by how much each looks like English.

How the Caesar cipher works

Each letter is shifted a fixed number of places along the alphabet. With a shift of 3, A becomes D and Z wraps round to C. Julius Caesar used a shift of 3. ROT13 (shift 13) is its own reverse: applying it twice gives back the original. ROT47 shifts all printable ASCII characters, including digits and symbols.

With only 25 possible keys, a Caesar cipher is easy to break. The cracker scores every shift against normal English letter frequencies (E, T, A, O, I, N are the most common) and shows the most likely answer first.

Frequently asked questions

How do I decode a Caesar cipher without the key?

Choose “Crack (try all shifts)”. Every shift is listed with the most English-looking result at the top.