Computational Thinking is a fundamental skill for the twenty-first century workforce. This broad target audience, including teachers and students with no programming experience, necessitates a shift in perspective toward Computational Thinking Tools that not only provide highly accessible programming environments but explicitly support the Computational Thinking Process. This evolution is crucial if Computational Thinking Tools are to be relevant to a wide range of school disciplines including STEM, art, music, and language learning. Computational Thinking Tools must help users through three fundamental stages of Computational Thinking: problem formulation, solution expression, and execution/evaluation. This chapter outlines three principles, and employs AgentCubes online as an example, on how a Computational Thinking Tool provides support for these stages by unifying human abilities with computer affordances.