In metal-catalyzed reactions involving multiple functional groups, the functionality preference of a catalyst dictates the identity of the initial adduct or intermediate that can direct the key propagating species and the formation of the final product. With this recognition, we developed a general and direct method using the fluorescence resonance energy transfer (FRET) principle.1 The FRET-based method has been successfully employed to quantify the functionality preference of diverse metal catalysts to their functionalities, such as alkynes, alkenes and allenes. The results enabled us to predict the chemoselectivity in metal catalyzed reactions such as hydroamination reactions of substrates possessing alkyne/alkene, alkyne/allene, or allene/alkene pair, along with answering the mechanistic issues such as the controversial reaction initiation in enyne metathesis. The newly found set of the catalyst-functionality preference might lead to new metal catalysis aided by much clarified reaction mechanisms.