ROT13 & Caesar Converter
ROT13 shifts Latin letters by 13 positions; Caesar mode lets you choose the shift. Both preserve case and leave other characters unchanged. These substitutions are easy to reverse and must not be used to protect passwords or confidential information.
Key features
- Choose ROT13 or Caesar encoding and decoding with a custom shift.
- Shift ASCII letters while preserving other scripts, numbers, whitespace, and emoji.
- Normalize negative or large shifts to a circular offset from 0 to 25.
How to use
- Choose ROT13 or a Caesar encoding/decoding mode.
- Enter text and, in Caesar mode, specify an integer shift.
- Run and copy the result. Caesar decoding applies the selected shift in the opposite direction.
Use cases
- Create word puzzles and simple quizzes.
- Read spoilers hidden using ROT13.
- Learn how alphabet substitution works.
Frequently asked questions
How do ROT13 and Caesar modes differ?
ROT13 always shifts by 13 and reverses itself when applied twice. Caesar modes use your chosen shift, with decoding moving in the opposite direction.
Does it change accented or full-width letters?
Only ASCII A–Z and a–z are changed. Accented letters, full-width letters such as Ａ, other scripts, and emoji are preserved.
Does ROT13 protect a secret message?
No. It is a keyless substitution that is trivial to reverse. It is not encryption for security or privacy.
Is there an input limit?
The limit is 100,000 UTF-16 code units. Process larger documents in smaller parts.
How are negative shifts or shifts above 26 handled?
Enter an integer from -1,000,000 to 1,000,000. Shifts wrap modulo 26: 29 equals 3, and -1 moves to the previous letter. ROT13 mode ignores the shift field.
Privacy
Input and results are processed in browser memory. This tool does not upload or save them; resetting or leaving the page clears them. Shared advertising and visitor analytics may operate separately, but individual input contents are not included in tool-use events.
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