An experiment was performed in order to assess the usability of CSRML Tool 2012 (CT’12), a tool to specify the requirements of CSCW systems. The effectiveness and efficiency of CT’12 were evaluated by means of several experimental tasks. Moreover, the user’s satisfaction was evaluated by using both a classical survey and analyzing the participants’ facial expressions when performing the experiments. Furthermore, this evaluation has been reported by using the ISO/IEC 25062:2006 , thus making its results comparable with other usability assessments which follow this international standard. Finally, details about how to develop a CASE toll for a Domain Specific Language was provided in a tutorial style.