Just in time for the US presidential election, Google is rolling out a "fact check" tag to its News service.

Google News aggregates stories from various sources (including PCMag), identifying them via labels like "highly cited," "featured," "opinion," "in depth," and now, "fact check."

Fact checking, once a job that was relegated to interns and entry-level reporters, "has come into its own," Google News head Richard Gingras wrote in blog post.

"Rigorous fact checks are now conducted by more than 100 active sites," he said, citing the Duke University Reporter's Lab. "They collectively product many thousands of fact-checks a year, examining claims around urban legends, politics, health, and the media itself."

Google's algorithms will determine which articles may contain fact checks using the schema.org ClaimReview system; it also looks for sites that follow commonly accepted criteria for fact checks. Publishers interested in applying to have their service included can find more details online.

News junkies in the US and UK will see new tagged reports in the expanded story box on the Web and in the Google News & Weather iOS and Android apps.

"We're excited to see the growth of the Fact Check community and to shine a light on its efforts to divine fact from fiction, wisdom from spin," Gingras said.

Google began labeling types of articles seven years ago, making it easier for readers to access a range of content. Earlier this year, it added a "Local Source" tag to highlight local coverage of major topics.

The news comes as Facebook is grappling with a spate of fake news in its trending section. Amidst concern that its trending news team was surfacing only liberal news, Facebook ditched human curators for algorithms. But its algorithms are apparently rather gullible. Facebook later joined an organization dedicated to tackling misinformation online, alongside Twitter and more than two dozen other tech and media titans.

In other Google search news, Search Engine Land reports reports that Google will soon favor its mobile search index over desktop. "Google is going to create a separate mobile index within months, one that will be the main or 'primary' index that the search engine uses to respond to queries," the blog says. The desktop index will remain but won't be updated as often as the mobile one.