This extension is for the most part just a wrapper around the Hypothesis client, an annotation viewer and editor that runs as an overlay in the browser. The client communicates with the Hypothesis annotation service that stores, searches, and displays annotations, and manages users and groups.

When you click on the extension’s button, the client is injected into the web page you are visiting. The client then gathers page metadata, including the URL and the web page title. It uses the API to ask the service for annotations that belong to the current host page, and paints them on the host page as highlights. The client also enables authorized users to publish and edit annotations on the service.

The client sets an auth cookie upon login to the service so you do not have to login again on the Hypothesis website. This cookie can also be read by the client so you do not have to enter your credentials again if you are logged in on the website already. You can modify your browser settings to decline cookies if you prefer, but you may not be able to fully experience the interactive features of the Hypothesis website and services.

The extension is granted the following permissions:
- Access your data for all websites: to inject the client code into the page and interact with the text on it, add and read annotations. It does not read or modify any other data.
- Access browser tabs: to maintain the state of the extension on windows or tabs you have open. This is also needed to tell you (via the extension badge) when a page you visit has been annotated. It does not keep track of what you do in the browser.

By default, the extension button displays the number of annotations found on the pages you visit, regardless of whether you press the button or not. To do so, the extension’s badge feature sends every URL you visit to the Hypothesis service. Hypothesis does not keep this browser history or does anything with it. You can disable this feature in the extension’s preferences if you find it distracting or if you do not wish the extension to make requests to the Hypothesis service for this data.

Hypothesis does not monitor, track or collect any of your personal data beyond what is necessary for creating, saving and reading your annotations, and it does not generate revenue from advertising or from selling metrics to third parties.

The Hypothesis privacy policy informs you of Hypothesis’ policies regarding the collection, use, and disclosure of personal information of users of their website and/or services. It can be found in https://web.hypothes.is/privacy/.