he Web site Stack Overflow was created in 2008 as a place for programmers to answer one another’s questions. At the time, the Web was thin on high-quality technical information; if you got stuck while coding and needed a hand, your best bet was old, scattered forum threads that often led nowhere. Jeff Atwood and Joel Spolsky, a pair of prominent software developers, sought to solve this problem by turning programming Q. & A. into a kind of multiplayer game. On Stack Overflow—the name refers to a common way that programs crash—people could earn points for posting popular questions and leaving helpful answers. Points earned badges and special privileges; users would be motivated by a mix of altruism and glory.

Within three years of its founding, Stack Overflow had become indispensable to working programmers, who consulted it daily. Pages from Stack Overflow dominated programming search results; the site had more than sixteen million unique visitors a month out of an estimated nine million programmers worldwide. Almost ninety per cent of them arrived through Google. The same story was playing out across the Web: this was the era of “Web 2.0,” and sites that could extract knowledge from people’s heads and organize it for others were thriving. Yelp, Reddit, Flickr, Goodreads, Tumblr, and Stack Overflow all launched within a few years of one another, during a period when Google was experiencing its own extraordinary growth. Web 2.0 and Google fuelled each other: by indexing these crowdsourced knowledge projects, Google could get its arms around vast, dense repositories of high-quality information for free, and those same sites could acquire users and contributors through Google. The search company’s rapacious pursuit of other people’s data was excused by the fact that it drove users toward the content it harvested. In those days, Google even measured its success partly by how quickly users left its search pages: a short stay meant that a user had found what they were looking for.

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