Caesar Cipher

Shift letters to encode or decode a Caesar cipher or ROT13. Free, runs entirely in your browser — no signup, and nothing you paste in is uploaded.

A Caesar shift moves each letter a fixed distance through the alphabet, which gives 25 possible keys — few enough that brute-forcing every one by hand takes about a minute. ROT13 is the special case of shifting by 13, which makes it its own inverse in a 26-letter alphabet.

It has no security value whatsoever and never did once frequency analysis existed; the letter distribution of the plaintext survives the shift completely. Its real uses are puzzles, teaching, and the original point of ROT13 online: hiding a spoiler from a casual glance rather than from anyone who wants to read it.