Mobile operating systems have evolved to provide increasing accessibility capabilities. However, mobile application developers are still restricted to deploy custom-made accessible applications or to extend limited and stereotyped accessibility services. In this paper, we present SWAT, an extensible framework that provides system-level content and event information to application developers. Its use is demonstrated in a multi-impairment case study achieving automatic row-column scanning with audio feedback. SWAT presents strengths usable in several other system-wide contexts that empower developers and users: adaptation, logging, testing and simulation.