We would like to present a case study of Yale University Library’s experience using DIY usability testing to identify and prioritize customizations to the out-of-the-box ArchivesSpace Public User Interface (PUI). In preparing Yale University Library’s PUI for launch, an implementation team was formed to identify custom settings and enhancements to meet user needs. Replacing the current Yale Finding Aid Database (YFAD), the PUI presents archival description in a very different way than Yale’s current, static, document-like online finding aids. Yale staff wanted the PUI to provide the same service as YFAD and improve on that service, all while creating a smooth transition between discovery platforms. However, an open source software designed to be be customized in-house and an internal lack of IT developer resources created challenges. To set priorities and make decisions about visuals, data display, site structure, and other enhancements, we conducted qualitative usability tests with users from our target audiences and tested the site for WCAG 2.0 compliance. Test results were compiled in a report with recommendations to address user confusions and frustrations. As is often the case, usability and accessibility issues overlapped, providing a stronger argument for key changes. After analyzing user feedback, we prioritized customizations and consulted with developers at Lyrasis to create a customized Yale PUI that meets our users’ needs while also contributing several enhancements to the PUI core code. Through iterative testing and prioritization, we’ve created a scalable method for capturing and incorporating user needs into our PUI customization.