The paper describes a meta language, called PSN (picture specification notation), for the specification of graphical notations in software engineering, and outlines the software tool building system for which it was designed. The latter is based on a prototype system which facilitated the rapid production of tools for processing textual notations. Since software project documents may now contain many graphical notations—data flow diagrams, Jackson system networks, and the like—the prototype has been extended to encompass graphical notations. The construction of tools for processing such notations is assisted by the syntactic correctness of documents containing them. This is guaranteed by a graphics editor which is driven by PSN specifications.