A Google Developer Tools developer uses Google's suite of tools to build, test, and debug web applications. They use Chrome DevTools to inspect and modify HTML, CSS, and JavaScript on live pages. They use Lighthouse for performance auditing and Workbox for service workers and caching. They may also use Puppeteer for browser automation tasks. Additionally, they could be involved in developing progressive web apps (PWAs), optimizing website speed, and ensuring website accessibility. Their overall goal is to create efficient, high-performing, and user-friendly web experiences, often collaborating with other developers, designers, and stakeholders throughout the process.