ROT13 — the self-inverse cipher
ROT13 became the standard internet convention for light obfuscation in the 1990s on Usenet newsgroups — specifically to hide spoilers so readers had to actively choose to see them. Because applying ROT13 twice returns the original text, there is no separate "encode" and "decode" mode — they are identical. This tool supports ROT13 plus other Caesar shifts (ROT1, ROT5, ROT18) and ROT47 for printable ASCII.
Shift reference
- ROT13 — shift 13 (A→N, N→A). Self-inverse. Standard internet spoiler obfuscation.
- ROT1 — shift 1 (A→B). Classic Caesar cipher style. Very easy to break.
- ROT5 — shift 5 for digits only (0→5, 5→0). Self-inverse for digits.
- ROT18 — ROT13 + ROT5 combined: letters shift 13, digits shift 5.
- ROT47 — shift 47 across all 94 printable ASCII characters (33–126). Encodes digits and punctuation too.
Frequently asked questions
Why does ROT13 encode and decode the same way?
The alphabet has 26 letters. Shifting by 13 twice completes a full rotation back to the start. A+13=N, N+13=A. It is its own inverse.
What is ROT47?
ROT47 rotates all 94 printable ASCII characters by 47 — exactly half of 94. Like ROT13 for letters, it is its own inverse and also encodes digits and punctuation.
What are practical uses for ROT13?
Hiding spoilers in forums, light email obfuscation from scrapers, puzzles, CS education for substitution ciphers. Not real encryption — provides no security.