CARMENES, the new ultra-stable high-resolution spectrograph at the 3.5 m Calar Alto telescope and the only one in its category that covers from 0.52 to 1.71μm in one shot, started its guaranteed time observations (GTO) in January 2016. Under GTO, CARMENES is monitoring approximately 300 selected M dwarfs for at least three years with the aim of finding rocky planets, perhaps habitable, orbiting around them. Those 300 GTO stars are the brightest and latest single M dwarfs observable from Calar Alto, which are carefully picked up from the CARMENES input catalogue, dubbed ''Carmencita'': CARMENES Cool star Information and daTa Archive. For each of the over 2200 M dwarfs in Carmencita, a team of German and Spanish astronomers involving PhD, MSc and BSc students has collected a large amount of information, compiled from the literature or measured by us with new data: accurate astrometry, spectral typing, photometry in 19 bands from the ultraviolet to the mid-infrared, rotational and radial velocities, X-ray count rates and hardness ratios, close and wide multiplicity data, kinematics, derived stellar parameters... The private online catalogue, including preparatory science observations (i.e., high-resolution imaging, low-and high-resolution spectroscopy), will be eventually public as a CARMENES legacy.