In order to reach valid and reliable test scores, various test theories have been developed, and one of them is nonparametric item response theory (NIRT). Mokken Models are the most widely known NIRT models which are useful for small samples and short tests. Mokken Package is useful for Mokken Scale Analysis. An important issue about validity is whether individual responses reflect individuals' characteristics truly or not. Examining individuals' score patterns with person-fit statistics is one way to detect invalid responses. PerFit Package can be used for detecting aberrant response patterns. This article explains and shows how to use Mokken and PerFit packages in RStudio.