XDebug is a tool for developers to gain insight into how PHP is executed. Using it for profiling is a very effective, fast and precise method to find bottlenecks in your WordPress site. In this talk I explain how to use it with Webgrind, how to find potential optimization targets, show examples of real cases when XDebug helped fix a performance problem and also explain what XDebug is not suitable for and what can be used instead. If you are not a developer, you’ll learn what XDebug is capable of and when to ask a developer to use it.