ROT13 Encoder / Decoder

ROT13 Encoder / Decoder

Convert text to ROT13 and ROT13 to text in one place. Type or paste anything and the rotated version appears instantly. Because ROT13 is its own inverse, the same text goes in either box and comes out readable again — the swap button simply moves the result back to the input.

How ROT13 works

ROT13 (“rotate by 13 places”) is a Caesar cipher with a fixed shift of 13. Each letter is replaced by the one 13 positions later in the alphabet, wrapping around after Z: A ↔ N, B ↔ O, M ↔ Z. Since the English alphabet has 26 letters, rotating twice brings you back to the start. Hello becomes Uryyb, and Uryyb becomes Hello. Upper and lower case are preserved; spaces, digits, and punctuation stay put.

Cipher variants

• ROT13 – the classic version that only rotates A–Z and a–z.
• ROT13 + ROT5 (sometimes called ROT18) – also rotates digits by 5, so 2026 becomes 7571. Useful when numbers would give away the answer.
• ROT47 – rotates every printable ASCII character between ! and ~. Hello, World! turns into w6==@[ (@C=5P, which hides numbers, symbols, and URLs too.

All three are self-inverse, so the selected cipher is used in both directions.

Where ROT13 is still used

ROT13 started on Usenet in the early 1980s as a polite way to hide spoilers and offensive jokes: readers had to deliberately decode a post to see it. Today you'll still meet it in puzzle and geocaching hints, CTF challenges, forum spoiler tags, programming exercises, and Easter eggs. Windows even stores some UserAssist registry values in ROT13. It is not encryption — for data that needs protection use real cryptography, and for transport encodings see Base64 Encode / Decode or the Morse Code Translator for something a little more old-school.

Tips

Paste an entire spoiler paragraph at once; line breaks are kept. If a decoded message still looks scrambled, try switching the cipher — a message full of odd symbols was probably ROT47, and one with shifted numbers likely used ROT13 + ROT5.