Roughly once a week, he and his team of about 16 adjust the complex computer code that decides what to show a user when he or she first logs on to Facebook. The code is based on “thousands and thousands” of metrics, Mr. Marra said, including what device a user is on, how many comments or likes a story has received and how long readers spend on an article.

The goal is to identify what users most enjoy, and its results vary around the world. In India, he said, people tend to share what the company calls the ABCDs: astrology, Bollywood, cricket and divinity.

If Facebook’s algorithm smiles on a publisher, the rewards, in terms of traffic, can be enormous. If Mr. Marra and his team decide that users do not enjoy certain things, such as teaser headlines that lure readers to click through to get all the information, it can mean ruin. When Facebook made changes to its algorithm last February to emphasize higher-quality content, several so-called viral sites that had thrived there, including Upworthy, Distractify and Elite Daily, saw large declines in their traffic.