A Flask developer designs and builds web applications using the Flask framework in Python. They create server-side logic, ensure high performance and responsiveness of applications, and integrate user-facing elements with server-side logic. They also implement data storage solutions, accommodate various security and data protection settings, and integrate multiple data sources and databases into one system. Moreover, they identify and fix bottlenecks and bugs, and maintain code quality, organization, and automatization. They work closely with front-end developers to integrate their work with the Python application, and often to develop RESTful APIs as well.