Inuit (short for “ In terface U sability I nstrumen t ”) is a new questionnaire you can use to assess the usability of your user interface. It has been designed to be more diagnostic than existing usability instruments like, e.g., SUS and for use with machine learning, all the while asking fewer questions than other questionnaires. This article explores how and why Inuit has been developed and why we can be sure that it actually measures usability, and reliably so.