The digital transformation of museums has elevated their websites from mere informational tools to dynamic platforms that foster cultural engagement, inclusivity, and preservation. This study evaluates the performance of 234 museum websites worldwide, focusing on critical dimensions such as accessibility, usability, SEO, and speed. By employing a comprehensive diagnostic framework of evaluation metrics, the research reveals disparities between mobile and desktop versions, highlights regional variations, and identifies key performance drivers. Generally, desktop sites outperform their mobile counterparts, underscoring the necessity for tailored optimization strategies that strike a balance between fast-loading, visually stable mobile pages and content-rich desktop experiences. A key contribution of this study is the development of an easy-to-adopt and inclusive evaluation framework that unites fragmented approaches, enabling museums of all sizes to enhance their digital presence. Furthermore, the research provides actionable insights for administrators, particularly those in resource-constrained institutions, through a cost-free, user-friendly toolkit that simplifies technical metrics and promotes internal staff capacity building in digital analytics. Ultimately, the findings help empower museums to bridge digital performance gaps while ensuring they continue to function as vibrant cultural hubs in a rapidly changing digital landscape.