COSTO (Component Study Toolbox) is the companion tool of the Kmelia language. It is a set of Eclipse-based plugins we developed to support the specification and analysis of Kmelia component systems. COSTO manages the Kmelia specifications and handles the verification of the primary properties (syntactic analysis, type checking, static analysis, …). The verifications of complex properties such as deadlock freeness, component or assembly consistency are delegated to other appropriate external tools (MEC, Altarica, Lotos/CADP, AtelierB, Rodin…).