Online ads are different from ads on traditional media, because they can be targeted only to specific groups and for short periods of time, making it difficult to scrutinize and fact-check them. This is particularly worrying in political campaigning.

To address this problem in December 2017 ProPublica launched a public and searchable database of political ads on Facebook. It includes each ad's targeting details.

The database was built thanks to PAC (Political Ad Collector), a tool, launched in September 2017, that allow Facebook users to automatically send ProPublica the political ads that they see in their News Feeds, through a plugin for Chrome or Firefox web browsers.

ProPublica's database refers only to the United States, but the tool is open source and was imported by newspapers and organizations in other countries including Denmark (Information), Finland (Aamulehti), Germany (Spiegel Online, Süddeutsche Zeitung and Tagesschau), Italy (OpenPolis), and Switzerland (Republik).

Tags: Media funding Social media Data journalism Open data