How atbash cipher works
The Atbash cipher is an ancient substitution cipher that maps each letter to its reverse position in the alphabet: A becomes Z, B becomes Y, C becomes X, and so on, so the first and last letters swap, the second and second-last swap, and so forth. It was originally applied to the Hebrew alphabet and appears in biblical texts.
Because the mapping is its own inverse (Z maps back to A, Y back to B), the same operation both encrypts and decrypts — there is no separate decryption step. Only letters are affected; upper and lower case are preserved and all other characters pass through unchanged.
Atbash has no key, so it offers no real security and is trivially broken. It survives today as a puzzle, a teaching example of monoalphabetic substitution, and a cipher used in geocaching and escape-room style games. All processing happens in your browser.