Caesar Cipher Encoder and ROT13
Encode and decode text with a Caesar cipher or ROT13, shifting each letter along the alphabet.
The oldest trick in cryptography
A Caesar cipher shifts every letter a fixed number of places along the alphabet — shift by three and A becomes D. ROT13 is the popular special case that shifts by thirteen, which conveniently means applying it twice returns the original. This encodes and decodes text with any shift, for puzzles, learning, or the light obscuring that ROT13 is traditionally used for.
Enter your text and a shift, and it is transformed.
Fun and educational, never secure
It is essential to be clear that this is not real security. A Caesar cipher has only twenty-five possible shifts, so it can be broken by simply trying them all, and ROT13 is not even meant to hide anything — it is a convention for lightly obscuring spoilers or punchlines so they are not read by accident. Treat both as a puzzle and a lesson in how ciphers work, never as a way to protect anything that actually matters, where real encryption like AES is required.
Common questions
Is a Caesar cipher secure?
No — with only 25 possible shifts it is trivially broken by trying them all. It is for puzzles and learning, not security.
What is ROT13 for?
Lightly obscuring text like spoilers so it is not read by accident. Applying it twice restores the original.
Is my text uploaded?
No. The conversion happens in your browser.