The ghstack extension is a Chrome add-on developed by ezyang.dev. It falls under the category of Browsers and is specifically classified under Add-ons & Tools. This free extension aims to enhance the GitHub user interface for users who have submitted pull requests using ghstack.

With the ghstack extension installed, users can expect a more streamlined GitHub experience. One of the key features of this extension is the removal of invalid merge buttons from the GitHub interface. This helps prevent confusion and ensures that only valid merge options are presented to the user.

Overall, the ghstack extension provides a valuable enhancement to the GitHub UI for individuals utilizing the ghstack tool. By removing invalid merge buttons, it helps users navigate the interface more efficiently and ensures a smoother workflow.