Domain-specific visual languages support high-level modeling for a wide range of application domains. However, building tools to support such languages is very challenging. We describe a set of key conceptual requirements for such tools and our approach to addressing these requirements, a set of visual language-based meta-tools. These support definition of meta-models, visual notations, views, modeling behaviours, design critics and model transformations and provide a platform to realize target visual modeling tools. Extensions support collaborative work, human-centric tool interaction, and multi-platform deployment. We illustrate application of the metatoolset on tools developed with our approach. We describe Tool Developer and cognitive evaluations of our platflorm and our exemplar tools, and summarise key future research directions.