A BioPAX developer works on the BioPAX (Biological Pathways Exchange) language, a standard for integration, exchange, visualization, and analysis of biological pathway data. They design and implement this ontology, ensuring it accurately represents biological concepts and relationships. They also develop tools and software that support BioPAX format, enabling researchers to convert, visualize, and analyze biological pathway data. They may also work on improving the language's compatibility with other bioinformatics tools and databases. Moreover, they are responsible for debugging, testing, and maintaining the BioPAX software to ensure its reliability and efficiency.