Open source software (OSS) development relies on diverse skill sets. Each skill is vital to OSS—software developers use problem-solving skills to build new features, software maintainers use organizational skills to manage an OSS project, and communication skills help everyone to effectively collaborate. However, to our knowledge, there are no tools to detect OSS-related skills. In this paper, we present a novel method to detecting OSS skills and prototype it in a tool called Disko. Our approach relies on identifying relevant signals, which are measurable activities or cues associated with a skill. Our tool detects how contributors 1) teach others to be involved in OSS projects, 2) show commitment towards an OSS project, 3) have knowledge in specific programming languages, and 4) are familiar with OSS practices. We then evaluate the tool by administering a survey to 455 OSS contributors. We demonstrate that Disko yields promising results: it detects the presence of these OSS skills with precision scores between 77% to 97%. We also find that 54% of participants would display their high-proficiency skills.