Shortly after a 7.8 magnitude earthquake hit Nepal on Saturday, social media services lit up with unverified reports of people trapped and buildings damaged. But how could humanitarian organizations know where to respond first? How could they know which accounts were actually true?

To weed out false rumors that can waste precious time, Justine Mackinnon has enlisted some local volunteers to use an experimental Web tool to crowdsource rumor verification as quickly as possible.

Mackinnon is the president of Standby Task Force, a group of volunteer “digital humanitarians” that becomes active after disasters at the request of international agencies and local relief organizations. The United Nations Office for the Coordination of Humanitarian Affairs has put Mackinnon’s organization in charge of a massive effort to sift through hundreds of thousands of tweets from people in Nepal to help workers identify priority areas.

Often, a large number of tweets coming from the same place and reporting the same general thing is enough verification, says Mackinnon. But sometimes the team encounters tweets “that don’t quite fit” with what the crowd is saying. Often these are untrue, but it is crucial that they be verified as quickly as possible in case they contain vital information. To do this, her group posts a “verification request,” in the form of a yes or no question, on a new Web platform called Verily (see “Preventing Misinformation from Spreading Through Social Media”).

Users can go to Verily’s website and read short tutorials on simple, established ways to verify things like the source of an image or the date and location of a report on a social network. They can answer yes-or-no verification questions about reports, provided they supply a piece of evidence supporting their answer—a corroborating photo, for example. Users can also share verification requests with their own social networks. Based on the evidence posted by Verily users, Mackinnon’s team can pass information along to relief organizations. The idea is to “crowdsource critical thinking,” says Patrick Meier, one of the creators of the tool and a co-founder of Standby Task Force.

Meier, who is director of social innovation program at the Qatar Computing Research Institute, previously served as the director of crisis mapping for Ushahidi, a Web platform developed in 2008 to monitor violence and riots during the fallout of a disputed Kenyan election. It has since been used to aggregate reports during unrest in the Middle East and after the devastating earthquake in Japan in 2011 (see “Crisis Mapping Meets Check In”). Ushahidi is now one of many organizations contributing to the data collection effort led by Standby Task Force.

Tools like Verily are only powerful if lots of people use them, and Mackinnon says that building a community has been the biggest challenge in Nepal, as well as during the first trial of the platform after a cyclone hit the nation of Vanuatu in March. For the past couple of days, the team has been teaching some 200 Nepali volunteers how to use the platform, with the hope that they can recruit others from their personal networks.