I Built an ISBN Decoder After Seeing Annas Archive's Visualization on HN

I Built an ISBN Decoder After Seeing Annas Archive's Visualization on HN ISBN Visualization hit the front page of Hacker News today ( 62 points ), and I fell into a rabbit hole. What is an ISBN? Most people just see it as "that barcode number on books." But there's a surprisingly elegant structure hidden inside. So I spent a few hours building a browser-based ISBN Decoder to make that structure visible. What's Actually in an ISBN-13? Take 978-0-13-468599-1 (Clean Code by Robert C. Martin): 978 - 0 - 13 - 468599 - 1 ▲ ▲ ▲ ▲ ▲ EAN Group Pub. Title Check 978 — The EAN prefix. Books use 978 or 979. That's why your ISBN starts the same as a grocery store barcode — it is a barcode. 0 — The group identifier. 0 and 1 both mean English-speaking countries (US, UK, Australia, Canada). 7 is China. 3 is German-speaking. 2 is French. There are over 200 group codes covering most of the world. 13 — The publisher code. Short codes = large publishers (O'Reilly, Penguin, etc). Long codes = small/independ