A Charles Web Debugging Proxy developer uses the Charles software tool to monitor, test, and debug web-based applications. They observe and analyze HTTP requests and responses between the client and the server, identifying issues in web traffic flow, session management, or data requests and responses. They also simulate network conditions, modify HTTP requests and responses, and validate responses, ensuring optimal application performance. Their role involves troubleshooting and resolving networking issues, enhancing web security, and improving application functionality. They work closely with development teams to ensure the smooth and efficient operation of web applications.