Hypothesis

Hypothesis puts notes on the live web instead of in a private library. Add the extension and a sidebar opens over any page you load — article, PDF, report — so the highlight is anchored to that URL rather than copied somewhere safer. Notes belong to groups: public ones anyone can read, private ones limited to members. That is why it has become standard equipment for cohort reading in universities, which is where the vendor pitches hardest, claiming more than three hundred institutions, and why it plugs into LMS platforms rather than asking students to keep a second account. The client is open source and there is an API, so annotations are not trapped behind the product.

Where it loses is anywhere a reader wants a queue instead of a layer. There is no offline reader and no tidy vault to hand to a colleague; finding your own annotation usually means going back to the page, and the open web does not promise to keep that page alive. Check three things before adopting it: institutional versus personal account terms, since the site is written for campuses and does not show individual pricing; group privacy defaults, because public annotation is the whole point and easy to trigger by accident; and the export route, which the API covers but which you should rehearse before entrusting years of reading to it.