Enables cysteine-type endopeptidase inhibitor activity. Involved in negative regulation of peptidase activity. Acts upstream of or within inhibition of cysteine-type endopeptidase activity; negative regulation of microglial cell activation; and positive regulation of myelination. Located in several cellular components, including Golgi apparatus; late endosome; and lysosome. Is expressed in several structures, including early conceptus and female reproductive system. Orthologous to human CST7 (cystatin F). [provided by Alliance of Genome Resources, Apr 2022]