CreepCheck is a Ruby library that provides an API for checking romantic age compatibility based on the popular half-plus-seven formula for determining when it is socially (in)appropriate for people to date based on their relative ages. It comes with a sample command line interface utility. Opinions vary on appropriate age differences in romantic relationships, but the half-plus-seven formula seems to approximate United States cultural biases about appropriate age differences pretty well. This library and utility package was originally created as a joke related to assessing the ap propriateness of relationships between characters in fictional contexts, such as in fantasy/sci-fi prose and roleplaying games. It is not intended to be treated as a substitute for moral fiber or individual judgement, and no guarantees are made about the likelihood one's family or local courts of law will approve of a given relationship on the basis of the age of one's partner even if "approved" by the half-plus-seven formula. This tool's major release version is published on April Fool's Day under the terms of the DPL, or Detachable Public License. It is intended for entertainment purposes only. It is not even particularly well-written.