Exemplars are powerful in clarifying assessment criteria, and their positive impacts on criteria understanding and performance have been empirically verified. However, the implementation modes are highly varied, resulting in a complicated class context which calls for further investigation. Less is known as to how exemplar-based instruction works in an online context. This qualitative study hence explores helpful contextual factors in an online exemplar-based class. Guided by Activity Theory, we collected students' perceptions of different contextual factors through questionnaires and semi-structured interviews and analysed the data through thematic analysis. The study found that among various contextual components, exemplars showing students' common problems were considered the most helpful, indicating that they could serve as an effective warning, provide immediate help and make the class more engaging. Reflective journal writing, access to dictionaries, and components valued in conventional classes were also found to be helpful. The findings contribute to more informative exemplar-based pedagogical decisions.