A HipChat developer is primarily responsible for creating and maintaining applications for the HipChat platform, a web service for internal private online chat and instant messaging. They use various programming languages and tools to design, test, and develop software that enhances user experience and meets business requirements. They also troubleshoot issues and ensure the application's stability and performance. Additionally, they work alongside other developers and stakeholders to integrate third-party services, improve the platform's functionality, and ensure the security of the application. They are also often involved in the entire software development cycle, from planning to deployment.