Caesar Cipher (ROT13)
The oldest known cipher: each English letter is shifted N places along the alphabet. ROT13 (shift 13) is its own inverse, perfect for hiding spoilers and light obfuscation.
How to Use
Paste text on the left. Only English letters (A–Z, a–z) shift; Korean, digits, symbols stay as-is.
Use the slider for any shift (0–25), or click "ROT13" to set 13.
The result updates live on the right. Caesar is symmetric: applying the same shift twice gets you back to the original (ROT13 + ROT13 = original).
FAQ
What is the Caesar cipher?
Said to date back to Julius Caesar — every letter is shifted N places. With shift 3, A→D, B→E, …, Z→C. Trivial to break, so it's used today only for learning, puzzles, and casual obfuscation.
What is ROT13?
Caesar cipher with a shift of 13 — exactly half the 26-letter alphabet. So ROT13(ROT13(text)) = text — same function decodes. Famous as the Usenet "hide spoilers" convention.
Korean / numbers / symbols?
The tool only shifts A–Z and a–z. Korean, digits, symbols, emoji, and whitespace pass through unchanged.
How do I decrypt?
Use the inverse shift: text encoded with N is decoded with 26 − N. ROT13 is special — 13 + 13 = 26, so the same shift works both ways.
Is anything sent to a server?
No. All conversion happens in your browser; nothing leaves the page.
