A Comscore AdEffx API developer works with Comscore's AdEffx platform, which provides ad effectiveness solutions. They use the API to integrate this platform with other software systems. Their duties include writing code to connect the API, troubleshooting issues, and ensuring seamless data flow between systems. They work with data related to ad effectiveness, including audience reach, brand impact, and sales lift metrics. This allows companies to measure the performance of their digital advertising campaigns, optimize their ad spend, and make data-driven decisions. They must also ensure the security and privacy of data processed through the API.