7-Azido-4-methylcoumarin is a highly sensitive and selective fluorogenic H2S probe. The aromatic azide moiety of AzMC is selectively reduced in the presence of H2S, producing the fluorescent 7-amino-4-methylcoumarin (AMC) with a concomitant increase in fluorescence with λex = 365 nm and λem = 450 nm. It is a photoaffinity labeling probe for the substrate binding site of human sulfotransferase 1A1 (SULT1A1). 7-Azido-4-methylcoumarin is a tool for monitoring the activity of pyridoxal-5'-phosphate (PLP)-dependent enzymes (e.g. cystathionine β-synthase (CBS), cystathionine γ-lyase (CGL) and tryptophan synthase (TS)) and to identify novel cystathionine β-synthase (CBS) inhibitors and activators.