This paper describes how the Cognitive Dimensions of Notation can guide the design of algorithmic composition tools. Prior research has also used the cognitive dimensions for analysing interaction design for algorithmic composition software. This work aims to address the shortcomings of existing algorithmic composition software, by utilising the more commonly used score notation interfaces, rather than patch based or code based environments. The paper sets out design requirements in each dimension and presents these in the context of a software prototype. These principles are also applicable for general music composition systems.