<p>This study investigates how collaboration is practically accomplished on large-scale online platforms, with scale understood qualitatively as asynchronous and fluid participation. Using Stack Overflow as an empirical case, it specifically examines how users collaboratively frame programming problems through questions, comments and iterative edits. Drawing on the practice-based perspective and ethnomethodology, the study uses trace ethnography and sequential analysis of selected Stack Overflow threads. Findings reveal that profession-specific shared objects (minimal reproducible examples) structured within the platform’s dual-space design, consisting of distinct question and commenting spaces, serve as crucial resources, enabling both immediate and future unknown contributors to understand and effectively engage in problem faming and problem-solving processes. Furthermore, the study identifies key interactional methods, i.e., standardized norm-enforcing requests and explicit referencing, which ensure mutual intelligibility of users’ comments and edits, essential for accomplishing collaboration at scale. The findings contribute to theoretical understandings of mass collaboration, offer design insights for platforms to facilitate the coordination of collaborative activities and provide recommendations for professional education to support productive participation in large-scale collaboration.</p>