Our knowledge as to how to solve software engineering problems is increasingly being encapsulated in tools. These tools are at their strongest when they operate in a pre-existing development environment that can provide integration with existing elements such as compilers, debuggers, profilers and visualizers. The first Workshop on Developing Tools as Plug-ins is a new forum in which to addresses research, ongoing work, ideas, concepts, and critical questions related to the engineering of software tools and plug-ins.