ROT13 & Caesar Cipher
Apply ROT13 or any Caesar shift (0–25) to text. Encode and decode letter-substitution ciphers instantly.
ROT13 (shift 13) is its own inverse — applying it twice returns the original text. For any other shift, decode by setting the shift to 26 − shift. Digits, punctuation, and spacing are left unchanged.
About ROT13 & Caesar Cipher
Apply ROT13 — or any Caesar cipher shift from 0 to 25 — to your text. ROT13 rotates each letter 13 places and is its own inverse, commonly used to hide spoilers and puzzle answers. Adjust the shift slider for a general Caesar cipher. Letters wrap within their case; digits and punctuation are left unchanged. Updates live.
All processing happens entirely in your browser using modern web APIs. Nothing is uploaded to our servers — your data stays local and private. Free to use forever.
Common use cases
- Hiding or revealing spoilers and puzzle answers (classic ROT13)
- Solving or creating Caesar cipher puzzles and CTF challenges
- Teaching how substitution ciphers and modular arithmetic work
- Lightly obfuscating text that should not be plainly readable
- Decoding a Caesar-shifted message by trying different shifts
How it works
Each letter is shifted by the chosen amount within its alphabet (A–Z or a–z) using modular arithmetic, so Z wraps back to A. ROT13 is simply a shift of 13 — applying it twice restores the original because 13 + 13 = 26. Non-letter characters pass through unchanged. To decode a shift of n, apply a shift of 26 − n.