A declarative specification for visualization may be improved. The declarative specification for the visualization may be identified and checked for appropriateness. This appropriateness check can be done by ensuring that the declarative specification meets a number of rules. The rules may be predefined and include rules that define best practices for visualizations. If a portion of the declarative specification violates one of the rules, it can be highlighted. In this way, the user can see how the declarative specification can be improved for visualization.