Using zone calculations in the FLAPW (the full-potential linearized augmented-plane-waves) model, information on the energy, charge and spin characteristics of Pt$_{1-x}$Ni$_{x}$MnSb alloys ($x$ = 0.0–1.0) is obtained. As established, with an increase in the concentration of nickel atoms in Pt$_{1-x}$Ni$_{x}$MnSb alloys, the interatomic space density of electrons decreases, covalent bonds weaken, and the cohesive energies of the alloys decrease. The dominant contributions to the formation of magnetic moments in Pt$_{1-x}$Ni$_{x}$MnSb alloys are provided by 3d electrons of manganese atoms. In alloys with $x \geq$ 0.50, a complete polarization of Fermi electrons is registered that converts these alloys to a half-metallic state.