ROT13 / Caesar Cipher
Letter-shift cipher. ROT13 is symmetric (apply twice to decode).
What is ROT13?
ROT13 is a Caesar cipher with a fixed shift of 13. Each letter is replaced by the letter 13 positions later in the alphabet (A↔N, B↔O, etc.). Because 13 is half of 26, ROT13 is its own inverse: applying it twice gives back the original text.
It's not encryption — anyone can decode ROT13 instantly. It's used as a courtesy obfuscation: hiding spoilers in forums, light puzzle creation, or as a teaching example for shift ciphers. Numbers and punctuation pass through unchanged.
Use cases
- Hide minor spoilers — wrap movie or game plot details in a forum or Slack post so readers decode opt-in.
- Encode trivia answers — Reddit comments with the answer below the question, ROT13 protects against accidental reveal.
- Quick obfuscation — disguise a guess or punch line so a single click reveals it.
- Teach symmetric ciphers — show how ROT13 is its own inverse, an easy intro to encryption concepts.
Examples
| Input | Result |
|---|---|
| Hello, World! | Uryyb, Jbeyq! (ROT13) |
| Hello, World! | Khoor, Zruog! (ROT3 / classic Caesar) |
Frequently asked questions
Is ROT13 secure?
No — it's trivially reversible. Don't use it for anything sensitive. Use real encryption (AES, public-key) for actual privacy.
Why is ROT13 popular if it's not secure?
It's a polite spoiler-hider. The convention is well-known online; readers can easily decode if they want to see the answer.
Can I use any shift, not just 13?
Yes — set the shift to any integer 1–25. ROT1 (shift 1) is sometimes called the 'Caesar cipher' specifically; the original cipher attributed to Caesar used shift 3.
Are non-letter characters preserved?
Yes. Numbers, punctuation, spaces, and emoji pass through unchanged — only A–Z and a–z are rotated.
Does the tool send anything?
No — the rotation runs in your browser.