Htmx is a JavaScript library that allows developers to access AJAX, CSS Transitions, WebSockets, and Server Sent Events directly in HTML. It provides a simple and powerful way to build modern user interfaces with hypertext. Htmx is small, dependency-free, and extendable, and has been shown to reduce code base sizes by 67% compared to React. The library is the successor to Intercooler.js and has dropped support for Internet Explorer.