A JAMstack developer is responsible for creating and maintaining web applications using the JAMstack architecture. This involves JavaScript for dynamic programming, APIs for server-side operations, and Markup for prebuilt templates. They focus on client-side rendering, reusability, and performance to create fast, secure, and scalable websites. They utilize static site generators, serverless functions, and headless CMSs, and often work with modern tools like React, Vue.js, and Netlify. They also ensure SEO optimization, and manage continuous deployment and version control systems. Besides, they handle user authentication, form handling, and other interactive elements using APIs.