IMS LD is a meta-language that can be used to specify a pedagogical method as a learning design. A learning design is a formal process model, encoded in XML, which can be played by any IMS LD-aware-player to learners online. In order to make it easy to edit learning designs, LD authoring tools are absolutely needed. Through a review of currently available LD authoring tools, we see that the development of LD authoring tools is still at an immature stage. This paper describes a LD authoring tool named CoSMoS, which can support editing learning designs at Levels A, B, and C. In this paper the main design ideas are presented and three design issues are discussed.