CompARE is a free on-line platform developed to help investigators to choose the primary endpoint of a Randomized Clinical Trial. It analyzes whether you should use a Composite endpoint as Primary endpoint in time-to-event studies, comparing different scenarios depending on different candidate endpoints. It is of great help when planning a clinical trial since it quantifies how efficient is a relevant subset of outcomes respect to a larger subset of outcomes. CompARE is a friendly free tool, and, although is internally programmed in R, users do not need knowledge of R, neither to have R installed in their computer. CompARE is based on the free software Tightly Integrated Knowledge Infrastructure (Tiki Wiki CMS/Goupware). Tiki allows to execute R routines by means of the pluginR, software written under the GNU/LGPL license. By means of web-page forms, users can easily introduce the required information, step by step. This information is saved in trackers allowing the code to be executed by the system and returning ad-hoc results depending on each case. Results from CompARE are shown by means of summary tables and plots. A history table saves each result to compare previous analyses. Moreover, conclusions and recommendations are given in written form as an aid.