A full-stack developer works on both the front-end and back-end of web applications. Key programming languages include HTML, CSS, and JavaScript for front-end development, enabling user interface design and interactivity. JavaScript frameworks like React or Angular are commonly used. For back-end, languages like Node.js, Python, Ruby, Java, or PHP are essential, depending on the tech stack. Knowledge of SQL or NoSQL databases (like MySQL or MongoDB) is also crucial. Full-stack developers often use version control systems like Git and are familiar with RESTful APIs, server management, and deployment tools to build and maintain robust web applications.