Dask is a pure Python library for parallel and distributed computing. It's designed with simplicity and flexibility in mind, making it easy to parallelize the kind of messy custom workflows that often show up in science. However, once you get something working, how do you debug or profile it? Debugging and profiling parallel code is notoriously hard! In this talk we'll cover the various tools Dask provides for diagnosing bugs and performance bottlenecks, as well as tips and techniques for resolving these issues.