Among the many new features introduced in Scala 3, one of the lesser-known ones is the error function. This seemingly simple function allows developers to define custom compile-time errors, marking a significant advancement in Scala's ability to ensure developer-friendly compile-time safety. However, every feature has its intricacies. To harness the full potential of the error function, one must delve deep into Scala's innovative compile-time programming techniques. It promises to be a captivating exploration. In this talk, Daniel will provide a tour of the error function, starting from the simple use cases and advancing to sophisticated yet developer-friendly error messages. Using a practical example, attendees will learn how and why to use the error function, as well as the accompanying compile-time programming techniques that will allow your error messages to really shine.