R-band magnitude (top left panel), 1.4 GHz flux density (top right panel), 0.2–12 keV flux (bottom left panel), and BlaST-derived synchrotron peak frequency (bottom right panel) as a function of redshift for all the 1007 5BZCAT sources without a counterpart in the 4FGL-DR4 Fermi-LAT catalog and with at least one X-ray counterpart in the 4XMM–DR13, 2CSC, 2SXPS, or eRASS1 catalogs. The different markers are linked to the 5BZCAT different blazar classes: BZQs (FSRQs) are plotted as pale gold circles, BZBs (BL Lacs) as violet squares, BZGs (BL Lacs with a significant contribution to the optical and infrared emission by the host galaxy) as orange hexagons, and BZU (blazars of uncertain classification) as green stars. As a reference, we also include in the plot those sources with a counterpart in the TeVCAT catalog (cyan diamonds), which are therefore known TeV emitters.