A key aspect of the design of,my software system is its architecture. An architecture description provides a formal model of the architecture in terms of components and connectors and how they are composed to-ether. COSA (Component-Object based Software Structures), is based on object-oriented modeling and component-based modeling. The model improves the reusability by increasing extensibility, evolvability, and compositionality of the software systems. This paper presents the COSA modelling tool which help architects the possibility to verify the structural coherence of a given system and to validate its semantics with COSA approach.