Caesar cipher & ROT13

How it works

Each letter is shifted forward through the alphabet by the chosen number of positions, wrapping from Z back to A; the shift is applied with modular arithmetic ((code - base + shift) % 26) so negative shifts used for decoding wrap correctly too, and characters that aren't letters — numbers, spaces, punctuation — pass through unchanged, with uppercase and lowercase handled separately so case is preserved.

FAQ

What's the difference between a Caesar cipher and ROT13?

None, mechanically — ROT13 is just a Caesar cipher with the shift fixed at 13. Because 26 letters split evenly in half, applying ROT13 twice returns the original text, which is why it's popular for hiding spoilers rather than real encryption.

Is a Caesar cipher secure for hiding sensitive information?

No — there are only 25 possible shifts, so it can be cracked by hand in seconds or brute-forced instantly by a computer. It's meant for puzzles and spoiler text, not real confidentiality.