Caesar Cipher
Shift any text by 1 to 25 letters to encode it, or use a negative shift to decode. ROT13 preset included. Free, instant.
How a Caesar cipher works
Pick a number between 1 and 25. To encode, shift every letter forward by that many positions: with a shift of 3, A → D, B → E, C → F, and so on. Z wraps back around to C. To decode, you shift the same amount in the opposite direction — so if a friend sent you a message encoded with shift 7, decoding it means using shift -7 (or, equivalently, shift 19, since shifts wrap modulo 26).
The ROT13 special case
ROT13 — Caesar with shift 13 — is the most famous variant. Because 13 is exactly half of 26, applying it twice returns the original text. That makes it a tidy little encoding for hiding spoilers, punchlines, or puzzle answers in plain text: anyone curious can decode it instantly, but it does not spoil the surprise for casual readers.
Cracking by sliding
Caesar ciphers are trivially breakable. If you receive ciphertext without the key, just slide the shift slider until the output becomes readable English — there are only 25 possibilities, so this takes about ten seconds. The tool above is designed to make this attack easy on purpose, because it is the most fun way to teach how weak monoalphabetic substitution is.
Try more codec tools
For other ways to encode text, try the Morse code translator, the Binary translator, or the Braille translator.