ROT13/ROT5 Combo Tool

How it is calculated

Each character is handled on its own. A letter from A to Z or a to z moves 13 places along the 26-letter alphabet and wraps around, keeping its case: (index + 13) mod 26. A digit from 0 to 9 moves 5 places along the ten digits and wraps: (digit + 5) mod 10. Everything else, such as spaces, punctuation and symbols, is copied unchanged. Accented letters and other non-English characters, for example the é in café, are also left as they are, because only the 26 basic Latin letters are rotated. Since 13 + 13 = 26 and 5 + 5 = 10, running the output through the tool again gives back the original text. This is a puzzle trick, not encryption.

Common mistakes

• Treating the output as secure. Anyone can reverse it in a second, so never use it to protect a password or personal data.
• Expecting accented or non-Latin letters to change. Letters such as é, ş or ж are left untouched, so parts of the text remain readable.
• Using plain ROT13 in another tool to decode this output. ROT13 alone leaves digits unchanged, so the numbers would come out wrong; the digit shift of 5 is needed as well.
• Applying the tool twice and expecting a different result. Two passes cancel out and return the starting text.
• Forgetting that spaces and punctuation are kept, which still shows word lengths and structure.