DKFZ-633 is a potent inhibitor of KLK6 and a KLK6-specific probe, exhibiting an IC50 of 250 nM against human KLK6. It selectively covalently labels the active state of KLK6, allowing for the successful pull-down and capture of endogenous active KLK6 from conditioned cell media. DKFZ-633 serves as an important tool for studying the function and regulatory mechanisms of KLK6 in head and neck cancer.