proper.io is an ad exchange. That means they work as a middleman between advertisers who buy ad space and publishers who sell ad space. proper.io has been authorized to sell the ad space on 422 publisher domains. You can view these domains below.
0.04% of the publishers we track have authorized proper.io.
This information is gathered by crawling ads.txt files on millions of websites. Ads.txt is an initiative developed by Google, the IAB and others to fight ad fraud.