Serine protease inhibitor selective for kallikreins. Efficiently inhibits KLK4, KLK5, KLK6, KLK7, KLK12, KLK13 and KLK14. Doesn't inhibit KLK8. {ECO:0000269|PubMed:20667819, ECO:0000269|PubMed:21439340}. This is the function of SPINK6 (serine peptidase inhibitor Kazal type 6, ENSG00000178172).