ROT13 Encoder & Decoder
ROT13 encodes text by rotating each letter 13 positions in the alphabet. A becomes N, B becomes O, and so on. Because the alphabet has 26 letters, applying ROT13 twice returns the original — so the encoder and decoder are the same operation.
About ROT13 Encoder
ROT13 (rotate by 13) is a simple letter substitution cipher: A→N, B→O, ..., M→Z, N→A, ..., Z→M. Numbers and non-letters pass through unchanged. Because 13 is exactly half of 26, applying ROT13 twice returns the original text.
ROT13 was widely used on Usenet newsgroups in the 1980s–90s to hide spoilers, punchlines, and content some readers might find offensive. It's not encryption in any security sense — it's trivially reversible — but remains useful for casual spoiler-hiding, puzzle creation, and as an introduction to substitution ciphers.
Our decoder is identical to the encoder — just run it again to reverse. Works on both uppercase and lowercase; punctuation and spaces pass through untouched.