  User interface design is a complex task that involves designers examining a
wide range of options. We present Spacewalker, a tool that allows designers to
rapidly search a large design space for an optimal web UI with integrated
support. Designers first annotate each attribute they want to explore in a
typical HTML page, using a simple markup extension we designed. Spacewalker
then parses the annotated HTML specification, and intelligently generates and
distributes various configurations of the web UI to crowd workers for
evaluation. We enhanced a genetic algorithm to accommodate crowd worker
responses from pairwise comparison of UI designs, which is crucial for
obtaining reliable feedback. Based on our experiments, Spacewalker allows
designers to effectively search a large design space of a UI, using the
language they are familiar with, and improve their design rapidly at a minimal
cost.
