Atbash is a monoalphabetic substitution that pairs the first and last letters, then works inward. This tool applies the Latin A-Z variant, preserves case, and leaves digits, punctuation, whitespace, and non-Latin characters unchanged.
The mapping A↔Z, B↔Y, through M↔N is its own inverse, so one operation both encodes and decodes. It is useful for historical demonstrations and puzzles, but fixed substitutions are easy to recognize and provide no modern security.
Hello -> Svool
Svool -> Hello