Background: Critical design configurations, so-called hotspots, have limited lithography process margins and are particularly sensitive to mask topography effects. Unfortunately, hotspot inspection at wafer-level is a costly, timeconsuming and non-exhaustive solution. On the other hand, accurate simulation of hotspots implies a very precise representation of the mask 3-D parameters which are challenging to measure directly on a reticle. Aim: In this work, we propose two complementary methods to characterize accurately hotspots without the need for wafer data. Approach: The first approach is based on Zeiss WLCD-2G aerial image metrology tool able to measure 2-dimensional high-resolution aerial images maps of any mask pattern across different focuses. The second approach uses rigorous simulations relying on very accurate mask parameters calibrated beforehand from the complete information contained in these high-resolution aerial images delivered by WLCD Results: The calibration of the mask parameters improves the matching between simulated and WLCD aerial images by almost 20% with an error of 2% (RMS). We showed with a few examples that hotspots discovered during the wafer patterning can be detected and characterized directly at the mask-level from the measured aerial images or from accurate resist simulations. Conclusions: The good matching between the rigorous simulation and WLCD as well as their capacity to predict hotspots cross-validates both methods. The calibration of the mask parameters also indicated that to achieve an even better matching our description of the mask proximity effect has to be more elaborated.