What if you published ground-breaking research. Would anybody notice? How would you know they noticed? Such questions aren't just for the narcissistic mad scientists among us. What if you funded the research? You'd want to know the impact. Altmetric tracks "article level mentions". These metrics are defined by the Public Library of Science (PLOS) as measuring usage, citations, social bookmarking and activity, media coverage (including blogs), ratings and discussion activity. The Altmetric API provides access to its metrics that are derived from its database of over 300,000 articles and over 8,000 journals.