A CometD developer designs, implements, and maintains web applications using the CometD software, a scalable HTTP-based event routing bus that uses an AJAX push technology pattern known as Comet. They utilize the CometD framework to enable real-time client-server communication, creating highly responsive and interactive web applications. Their duties involve writing server-side application logic, implementing CometD APIs, troubleshooting, and fixing bugs. Furthermore, they ensure the scalability and reliability of applications, manage data synchronization between servers and clients, and work towards enhancing user experience. They often collaborate with other developers and stakeholders to meet specific project goals.