  Selecting a UI element is a fundamental operation on webpages, and the ease
of tapping a target object has a significant impact on usability. It is thus
important to analyze existing UIs in order to design better ones. However,
tools proposed in previous studies cannot identify whether an element is
tappable on modern webpages. In this study, we developed Tappy that can
identify tappable UI elements on webpages and estimate the tap-success rate
based on the element size. Our interviews of professional designers and
engineers showed that Tappy helped discussions of UI design on the basis of its
quantitative metric. Furthermore, we have launched this tool to be freely
available to external users, so readers can access Tappy by visiting the
website (https://tappy.yahoo.co.jp).
