ROT13 shifts every letter 13 places through the alphabet. It is often used to hide a puzzle answer or spoiler from a casual glance. There is no key to choose: applying ROT13 again reveals the message.

One mapping for both directions

The alphabet has two halves of 13 letters. Move a letter 13 places to find its partner; move it another 13 and you are back where you started. That is why Encode and Decode give the same result for the same input.

First halfSecond half
ABCDEFGHIJKLMNOPQRSTUVWXYZ

Apply once

InputAbc Nop!
SettingsFixed shift 13; uppercase A–Z; preserve nonletters
Expected resultNOP ABC!
Try this method

This tool first turns Abc Nop! into uppercase ABC NOP!. ROT13 gives NOP ABC!; applying it again returns ABC NOP!. The space and exclamation mark stay in place, but the original capitalization is not restored.

Follow a single letter

  1. Find B at index 1.
  2. Add 13 to get 14.
  3. Read index 14 as O.
  4. Repeat with O: 14 + 13 = 27, and 27 mod 26 = 1, returning B.

Try one yourself

Apply ROT13 to READ ME, then apply it to the result. Which punctuation or spacing changes?

Keep exploring

Caesar cipher toolHow modulo 26 wraps around the alphabetHow text conversion and preparation work