Work out caesar cipher shift instantly with clear inputs, formula shown and shareable results.
The Caesar cipher shifts each letter a fixed number of positions modulo 26, leaving non-letters untouched. Its keyspace is just 25 usable shifts, so exhaustive search is instant, and frequency analysis identifies the shift from a single line of ciphertext. It survives as a teaching example of modular arithmetic and of why key size alone determines nothing if the keyspace is tiny.
Caesar shift
encrypt: c = (p + k) mod 26; decrypt: p = (c - k) mod 26, applied to letters only
A Caesar cipher with shift 13, which is its own inverse because 13 + 13 = 26. It is used to obscure spoilers, not for security.
Try all 25 shifts, or compare letter frequencies against the language's expected distribution. Both take seconds by hand.