Context: A significant effort has been devoted to the design and implementation of various domain-specific modeling languages (DSMLs) for the software agents domain. Problem: Language usability is often tackled in an ad-hoc way, with the collection of anecdotal evidence supporting the process. However, usability plays an important role in the productivity, learnability and, ultimately, in the adoption of a MAS DSML by agent developers. Method: In this chapter, we discuss how the principles of The “Physics” of Notations (PoN) can be applied to improve the visual notation of a MAS DSML, called SEA_ML and evaluate the result in terms of usability. Results: The evolved version of the language, SEA_ML++, was perceived as significantly improved in terms of icons comprehensibility, adequacy and usability, as a direct result of employing the principles of PoN. However, users were not significantly more efficient and effective with SEA_ML++, suggesting these 2 properties were not chiefly constrained by the identified shortcomings of the SEA_ML concrete syntax.