ROT13 Encoder/Decoder

This cipher tool implements ROT13 (rotate by 13 places), a simple letter substitution cipher that replaces each letter with the letter 13 positions forward in the alphabet. Since the English alphabet has 26 letters, applying ROT13 twice returns the original text—making it a self-inverse function where encoding and decoding are identical operations.

The algorithm processes each character independently: uppercase letters (A-Z) and lowercase letters (a-z) rotate within their respective ranges using modular arithmetic, while numbers, spaces, and punctuation pass through unchanged. Configurable settings allow custom rotation amounts (ROT1 through ROT25) for Caesar cipher variants, case preservation toggles, and non-alphabetic character handling.

Visual alphabet mapping displays the substitution table for educational reference. Common uses include hiding spoilers in online discussions, puzzle games, CTF challenges, and demonstrating basic cryptographic concepts—though ROT13 provides no real security and should never be used for protecting sensitive information.