Upcoming telescopes such as the James Webb Space Telescope (JWST), the European Extremely Large Telescope (E-ELT), the Thirty Meter Telescope (TMT) or the Giant Magellan Telescope (GMT) may soon be able to characterize, through transmission, emission or reflection spectroscopy, the atmospheres of rocky exoplanets orbiting nearby cool stars called M dwarfs. In this context, the modeling of its potential atmosphere is an essential step prior to observation. Global Circulation Models (GCMs) offer the most detailed way to simulate planetary atmospheres. However, intrinsic differences exist between GCMs which can lead to different climate prediction and thus different estimation of the detectability of exoplanet atmospheres. We present a protocol to inter-compare planetary GCMs and present the first results of the intercomparison using the TRAPPIST-1e planet as a benchmark. Currently, there are four participating models (LMDG, ROCKE-3D, ExoCAM, UM), however this protocol is intended to let other teams participate as well.