The results of a comprehensive study of a compact UV-preionized XeCl laser are presented. The subjects of this study were: discharge voltage and current measurements, dye laser probing of the active medium, and the mass spectrometry of gas mixture degradation products. It is shown that the gas lifetime was significantly improved when the laser was operated with BCl3 as a halogen donor instead of commonly used HCl. By the dye laser absorption and gain probing, the temporal and spatial dependences of the densities for several plasma components, Ne*, Xe*, Xe+*, Cl−, XeCl* and of ground state boron atoms were measured. Some aspects of plasma kinetics for uniform and constricted phases of the discharge are discussed. By the mass spectrometry of gas mixture degradation products on long-term operation of the laser device several gaseous (N2, O2, CO2, H2O, C2H4) and solid (NiCl2, H3BO3) products were detected in the laser chamber. NH4Cl was determined to be a stable fraction of the deposits on optics surfaces. The reasons for the improvement of gas lifetime for BCl3-containing gas mixtures are discussed.