The design of Tumblr, the blogging tool and social network, is guided by feeling. In particular, the feelings of David Karp, the company’s 26-year-old founder, whose instincts tend to run counter to current Web conventions. Tumblr does not display “follower” counts, for example, or other numerical markers of popularity that are viewed as crucial social-media features, because Karp finds them “really gross.” The culture of public friend-and-follow reciprocity that theoretically expands a social networking service can, in his view, “really poison a whole community.”

Possibly such a view of Internet culture could be arrived at by way of deliberate study of online group behavior. But that’s not how Tumblr was made. “David built it for himself,” John Maloney, until recently the company’s president, told me. Marco Arment, Karp’s first employee, who participated directly in the service’s creation, put it even more succinctly: “Tumblr is David.”

I met Karp in Tumblr’s offices in the Flatiron district in New York. In his standard uniform of Jack Purcell sneakers, dark pants and a hoodie over a patterned shirt, Karp was polite, upbeat, inclusive and big on eye contact. Asked a question about competitors, he answered: “The last thing we want to do is compete with someone. That’s for bankers.” Karp likes to talk about Tumblr less as a business than as a “platform for creativity.” And indeed, it has been used to make more than 60 million blogs — among them a visual scrapbook kept by Michael Stipe; silly meme-blogs like Hey Girl, It’s Paul Ryan; and the clever graphic analysis that became the recent book “I Love Charts” — drawing a combined 17.5 billion page views a month.

The trick is making page views equal money. “Pretty much every large tech company today,” Karp said, is essentially “metrics driven.” Google, Twitter, Facebook: they’re obsessed with “optimizing” services, design, functionality and aesthetics through constant testing and tweaking. That ability to optimize and (not incidentally) monetize user experiences by reacting to microlevel data is the essence of Web-business magic, as it is generally understood.