Samples with tungsten (W) and tungsten–yttrium (Y) coatings on molybdenum were exposed to plasmas simulating the divertor conditions of ITER. The exposed surfaces were studied using in-situ laser induced breakdown spectroscopy diagnostics (LIBS) and the results were compared to those obtained by other surface characterization methods. Our results show that LIBS is a reliable technique for in situ monitoring of erosion, deposition, and fuel retention processes under reactor-relevant conditions. In the regions of the highest gross erosion the thickness of the remaining tungsten layer is thinnest and at the central part of samples both mixing and deposition of components took place. LIBS also allowed reliable recording of D retention. D accumulation is influenced by the surface temperature as well as by the surface irregularities.