Alf is an action language designed to be used as a textual notation for specifying detailed behaviors in the context of an executable UML model. The implementation of Alf within MagicDraw, a leading commercial tool for modeling using the Unified Modeling Language (UML) from No Magic, Inc., aims to support the practical application of Alf in real-world uses of executable UML modeling. It includes syntax-aware editing and validation of Alf text, with valid code automatically and transparently compiled into UML activity models. The resulting models are fully integrated within the wider UML modeling context (such as a containing state machine or class model), and they can then be executed as part of full system simulation scenarios. The Alf compiler also tracks the dependencies of all Alf text on other UML model elements, allowing for the automatic re-checking and re-building the Alf code as necessitated by changes in referenced elements. The goal is to provide an IDE-level experience for the easy entry and maintenance of Alf code within an overall executable UML model.