In the presented work a fast frequency domain measurement system to determine group delay (GD) and group delay dispersion (GDD) of optical coatings is proposed. The measurements are performed in situ directly on moving substrates during the thin film coating process. The method is based on a Michelson interferometer, which is equipped with a high power broad band light source and a fast spectrometer. Especially for the production of chirped mirrors it is advantageous to obtain group delay and group delay dispersion data of the last layers. This additional information allows for online corrections of coating errors to enhance the precision of complex interference filters for short pulse applications.