The living cell of a host organism provides the conditions where viruses replicate and produce new viral particles. That can infect all living organisms, including animals, plants, and other microorganisms. Viruses often have high mutation rate, which allows them to change and adapt very quickly. Rapid and accurate diagnostic methods are crucial, particularly for agricultural applications for detecting fruit viruses. This chapter provides a critical analysis of the widely used rapid and sensitive on-site diagnostic tools for detecting fruit viruses. It also highlights challenges and limitations of these tools. Recent advances in portable technologies have made field testing more practical. Such as immunoassay detection generally offers high sensitivity and specificity, and it gives results within some time. Furthermore, some immunoassays, like the lateral-flow assay, give results within minutes. On the other hand, nucleic acid-based detection techniques offer high sensitivity; however, they are time-consuming, costly, and require molecular biology expertise to obtain accurate results. Beyond these methods, the application of next-generation sequencing (NGS) is a sophisticated diagnostic approach that gives very specific results. NGS allows simultaneous processing of vast numbers of DNA or RNA sequences with high speed and accuracy. This enables comprehensive analysis by fragmenting, amplifying, and detecting sequences through high-throughput, parallel processing technologies. Nucleic acid-based techniques are precise but demand more resources and experts. NGS is very costly and complex, but it offers high specificity and sensitivity. Collectively, these tools help identify infected plants quickly, allowing growers to remove or manage diseased trees before the virus spreads further.