When you type the term “bike jersey” into the search field at Etsy.com, most of the results you get are, in fact, bike jerseys. 

That may sound like “dog bites man” news. But not long ago, running such a search at this e-commerce site for handmade and craftsy goods would have yielded a torrent of irrelevant results—a necktie covered with tiny embroidered bikes, a baseball jersey, a vintage New Jersey bicycle license plate. Given the high proportion of sales driven by first-page rankings from a desktop search, useless results mean lost revenue, says Etsy technology chief Mike Fisher: “I’ve got to be very narrow very quickly, or else I lose you.”