Designing usable APIs is critical to developers’ productivity and software quality, but is quite difficult. Understanding how the API is used by analyzing client code at scale to discover usability issues with the APIs is even harder. In this paper, we focus on “boilerplate” code, which a number of experts in API design have said can be an indicator of API usability problems. We investigate what properties make code count as boilerplate, the reasons for boilerplate, and how programmers can reduce the need for it. We propose MARBLE, a novel approach to automatically mine boilerplate code from a large set of client code. MARBLE adapts existing techniques, including an API usage mining algorithm, an AST comparison algorithm, and a graph partitioning algorithm. We evaluate MARBLE with 13 Java APIs, and show that our algorithm successfully identifies both already-identified and new boilerplate code instances.