Before the era of established discovery systems like EDS and VuFind, the Staats- und Universitätsbibliothek Bremen took a solitary step in 2000 by developing its own discovery system that includes various document types -- not just physical books. This talk will discuss the process of developing an open-source patron service using Okapi endpoints, highlighting the challenges encountered along the way. The focus will also be on the inclusivity of our system, designed to be usable beyond our library, inviting wider adoption. Despite the hurdles, the project underscores the potential for libraries to craft tailored solutions that meet their unique needs. This presentation aims to share insights and experiences from our transition, offering a realistic perspective on the possibilities and pain points of library system development. Our Patron Service will be released as Open Source in Summer 2024: https://gitlab.suub.uni-bremen.de/public-projects/folio/patron-service