<p>Viral diseases remain a persistent global health threat, causing millions of deaths annually, with disproportionate impacts on populations in low- and middle-income countries and marginalized communities. Molecular diagnostics offer high accuracy for viral detection; however, their use remains largely confined to centralized laboratories, creating gaps in disease surveillance, clinical management and outbreak response. In this Review, we assess the current landscape of viral diagnostics, revealing disparities in test availability across viruses and inequities in global access, and emphasizing the need for decentralized, context-appropriate diagnostic solutions capable of supporting viral detection across diverse healthcare settings. We describe key performance criteria to assess diagnostics for use in decentralized settings, examining five molecular diagnostic platforms, including polymerase chain reaction (PCR)-based technologies, isothermal amplification, clustered regularly interspaced short palindromic repeats (CRISPR)-based diagnostics, synthetic biology approaches and portable sequencing. Finally, we outline key considerations for the translation of molecular diagnostic tests, including context-adapted design, strategies to address viral diversity and evolution, rigorous test validation, simplified sample processing, and integrated result interpretation and connectivity.</p>