GitHub Hovercard is a browser extension that enhances GitHub with rich hovercards for user profiles, repositories, issues, pull requests, comments, and commits. When hovering over a link on GitHub, it fetches data from the GitHub REST API and displays a tooltip with relevant details such as follower counts, star counts, README previews, issue status, and commit information. The extension also supports authenticated actions like following/unfollowing users and starring/unstarring repositories via a user-supplied access token. The extension is implemented as a monolithic content script that runs on all GitHub pages. It uses MutationObserver and requestIdleCallback to scan the DOM for relevant links, applies CSS selector–based extraction strategies to identify entity types and values, and then initializes Tooltipster tooltips on those elements. Data is fetched via jQuery AJAX and cached per entity type. The UI is rendered using Mustache templates with inline emoji and Octicons. The project includes separate extension packages for Chrome, Firefox, Edge, and Safari, each duplicating core files like jQuery, Mustache, Tooltipster, and the main hovercard script. A userscript variant is also provided. While the extension is functionally complete and has a loyal user base, the codebase exhibits significant technical drift and maintenance risks. Dependencies are outdated (jQuery 3.1.0, Tooltipster 4.0.0rc23), GitHub DOM selectors are fragile and likely to break with UI updates, API preview headers may be deprecated, and the same source files are duplicated across multiple extension directories without a shared build system. No tests are present, and the project appears to have received no recent commits, making it a candidate for forking or modernization.