GUMICS-4 is a global magnetosphere–ionosphere coupling simulation based on global MHD magnetosphere and an electrostatic ionosphere. Here we review the development history, design and technical features of GUMICS-4 as well as a number of its postprocessing tools. We also compare GUMICS-4 predictions with observations for magnetopause distance, interplantary magnetic field penetration in the magnetotail, ionospheric field-aligned current pattern and other quantities. Based on the comparisons we can conclude that to a useful extent and with certain limitations, GUMICS-4 can reveal the detailed spatiotemporal behaviour of the magnetosphere–ionosphere system under given solar wind forcing.