Show HN: Extend UI – open-source UI kit for modern document apps

A new Show HN project, Extend UI, is pitching itself as a ready-made kit for document-heavy apps: think viewing PDFs, Word files, spreadsheets, and CSVs, plus file uploads, electronic signatures, and those flashy little boxes that point to exact parts of a document. On paper, it sounds like a dream for anyone building apps around files. In the comments, though, the real show begins: admiration, nitpicking, and a mini revolt over what’s missing.

The loudest complaint? A classic internet favorite: “Why is this only for React?” One commenter basically declared it “bad for the web” that the project doesn’t support other ways of building sites, while another was annoyed that it apparently didn’t say clearly enough that these were React components in the first place. Translation for normal humans: some people loved the idea, but got immediately grumpy that it seemed built for one club instead of everyone.

Not everyone came to throw tomatoes. One commenter was genuinely impressed by the spreadsheet viewer and asked how on earth it was built, with a tone that screamed, “This must have been a nightmare.” Another gave the bounding-box document highlights a respectful nod, then launched into the kind of deeply caffeinated concern only developers can love: how do those boxes behave when you zoom and scroll? And then came the most brutal review of all, courtesy of mobile Safari: “This page could not load.” Ouch. Nothing kills launch-day vibes faster than your demo face-planting on an iPhone.