Enables serine-type endopeptidase inhibitor activity. Involved in cellular response to BMP stimulus; negative regulation of neural precursor cell proliferation; and positive regulation of glial cell differentiation. Located in plasma membrane. Biomarker of liver cirrhosis. Orthologous to human SPINT1 (serine peptidase inhibitor, Kunitz type 1). [provided by Alliance of Genome Resources, Apr 2022]