A killer feature would be a combination of tying into the "share to" functionality on mobile + browser plugins that replicate this.

The Story: You're browsing the University of Chicago Press, Yale Press, Scholastic, Amazon, whatever, and see a book you'd like to add in Hardcover. Right now, you scan the page for an ISBn, copy it, open Hardcover's website or app, paste in the search, etc.

It would be really great to be able to tie this into mobile's share-to feature as well as PCs with browser plugins.

I believe on Android this is called an "intent."

So the user would, say, have their email app open, be reading an email from a press advertising their latest books, and you click through to a book to read more.

Wow, it looks great! I'd like to read that when I have time. They tap "share" in their mobile browser, which brings up the app list, and you tap Hardcover from the list.

The Hardcover app loads up with that book loaded the same way it does if you search for the book specifically in Hardcover.

You tap "want to read" and hit the back button and you're back to your email.

The hardest part is probably the logic for extracting what to search for (search for ISBn probably easy since it's a mathematically defined format, 13 digits where the 13th is a checksum), extracting author and title might be slightly harder and rely on website quirks.