Universal health coverage (UHC) aims to ensure access to quality health care for all individuals, without causing financial hardship. In upper middle-income countries like Paraguay, UHC can be achieved by strengthening the primary healthcare (PHC) system. However, current studies primarily focus on expanding the universality of PHC as a key aspect of UHC, with limited research evaluating the service readiness of healthcare facilities providing PHC services in such settings. This cross-sectional, quasi-experimental study aimed to characterize the service readiness of public healthcare facilities in Paraguay using the WHO Service Availability and Readiness Assessment (SARA) tool. The study sought to identify areas for improvement and to inform health policies and decisions to enhance the quality and accessibility of healthcare services. Additionally, it addressed the need for standardized assessment tools to evaluate and improve the capacity of PHC facilities in countries like Paraguay.