Facebook has assembled a small army of fact-checkers. Too small.

People use smartphones in Mumbai, India, on Friday, March 28, 2019. Based on the early tallies, as many as 60 percent of India’s 900 million eligible voters are expected to cast ballots between now and May 19, as the center-left Congress Party tries to seize power from the right-wing Bharatiya Janata Party. As in other elections around the world, paid hacks and party zealots are churning out propaganda on Facebook Inc. and the company's WhatsApp messenger, along with Twitter, YouTube, TikTok, and other ubiquitous communication channels. Photographer: Dhiraj Singh/Bloomberg

One of the operations most vital to Facebook Inc at this moment is a world away from its Menlo Park, California, headquarters, and in more ways than one. 

Instead of the sprawling roof gardens and upscale cafés packed with Silicon Valley’s latest health fads, this cramped Mumbai office has worn carpets and fading walls lined with exposed electrical ducts.