A Chrome Development Tools developer uses Google Chrome's built-in set of web authoring and debugging tools, known as DevTools, to create, test, and debug websites and web applications. They manipulate the DOM and CSS styles directly, diagnose issues quickly to ensure smooth performance, and understand the impact of a page on network performance. They also debug JavaScript using breakpoints and observe JavaScript expressions in real-time. They can also simulate mobile devices for responsive web design testing. These developers help improve the user experience by ensuring websites and applications function correctly and efficiently.