This repository holds the supplementary materials for Lukoff et al. (2021) "How the Design of YouTube Influences User Sense of Agency." It contains: 1. **Appendix_I_YouTube_Screenshots.pdf** - Screenshots of the design mechanisms in the YouTube mobile app at the time that this research was conducted (May 2020). 2. **Appendix_II_Redesign_Mockups.pdf** - Contains: (a) A table of all seven redesigned mechanisms of YouTube, with descriptions; (b) More details about the search redesign; and (c) 21 mockup images, three versions (low, medium, and high-control) for each of the seven redesigned mechanisms. 3. **Survey** - Eligibility survey and full survey for Study 1 4. **Interview Protocol** - Protocol for the interview in Study 2 5. **Interview Debriefing Form** - Debriefing form completed by interviewers after conducting an interview in Study 2 Paper abstract: *In the attention economy, video apps employ design mechanisms like autoplay that exploit psychological vulnerabilities to maximize watch time. Consequently, many people feel a lack of agency over their app use, which is linked to negative life effects such as loss of sleep. Prior design research has innovated external mechanisms that police multiple apps, such as lockout timers. In this work, we shift the focus to how the internal mechanisms of an app can support user agency, taking the popular YouTube mobile app as a test case. From a survey of 120 U.S. users, we find that autoplay and recommendations primarily undermine sense of agency, while playlists and search support it. From 13 co-design sessions, we find that when users have a specific intention for how they want to use YouTube they prefer interfaces that support greater agency. We discuss implications for how designers can help users reclaim a sense of agency over their media use.*