Abstract. In this paper, we describe the design of the coupling library Jcup and report its various applications including the coupling between the global atmospheric and oceanic models with different grid systems. Jcup is a software library mainly focused on weather/climate models and was developed for the purpose of coupling components of various models. Jcup has flexibility in application to an unspecified number of components of earth system models. In order to achieve high order safety and versatility, we divided 5 the processes of a general coupling program into processes of changing and not changing the values of the data, and placed the former outside the program and under the control of the user. As a result, Jcup has two features: 1) that the correspondence relationship of grid indexes is used as input information, and 2) that the user can implement an arbitrary interpolation code. Jcup was applied to atmosphere–ocean coupling, IO component coupling, and seismic model–structure model coupling, and the validity and usefulness of the design were demonstrated.