CrySL is a Domain Specific Language (DSL) that is utilized by CogniCrypt to assess correctness of API usage during application analysis. In this session we present the details of CrySL before guiding participants through building their very own CrySL rule. This session will also demonstrate the generalizability of CrySL; it is not inherently designed to specify correctness of cryptographic APIs and therefore can be used to define correctness for other API usages as well. This will be an interactive session, so make sure to bring a laptop! It is recommended to preview the session setup instructions prior to attending.