Long-term light curves of Mrk 421 obtained from the radio to the TeV between December 14, 2012, and April 18, 2018. From top to bottom: FACT (E_Th ∼ 700 GeV), Fermi-LAT (0.1–300 GeV), MAXI (2–20 keV), Swift/BAT (15–50 keV), Swift/XRT (2–10 keV), Swift/XRT (0.3–2 keV), Swift/UVOT UVM2, V-band optical observations, and radio observations at 15 GHz. Flux measurement errors are denoted as vertical grey bars. Points with signal-to-noise ratio lower than two are coloured red (see Sect. 2 for details on the cleaning procedures). For the FACT light curve, there are 177 (out of 580) such points. For the Fermi-LAT light curve, 95% flux upper limits (TS < 25) are shown with triangles. For the FACT light curve, the flares listed in Table 1 are highlighted in grey.