ECDAR: an environment for compositional design and analysis of real time systems. We present Ecdar a new tool for compositional design and verification of real time systems. In Ecdar, a component interface describes both the behaviour of the component and the component’s assumptions about the environment. The tool supports the important operations of a good compositional reasoning theory: composition, conjunction, quotient, consistency/satisfaction checking, and refinement. The operators can be used to combine basic models into larger specifications to construct comprehensive system descriptions from basic requirements. Algorithms to perform these operations have been based on a game theoretical setting that permits, for example, to capture the real-time constraints on communication events between components. The compositional approach allows for scalability in the verification.