In one embodiment, a method includes identifying, by a search engine of an online social network, web domains external to the online social network. The method includes accessing domain-quality signals associated with each web domain. At least one of the domain-quality signals includes a measure of activations of social plug-ins of the online social network available on webpages of each web domain, a social plug-in being an executable script providing an activable user-interface element for interacting with the online social network from the webpage. The method includes calculating, for each web domain, a domain ranking based at least in part on the domain-quality signals associated with the web domain. The method includes identifying, by the search engine, some of the web domains as low-quality web domains to avoid accessing based at least in part on the domain rankings of the web domains not satisfying a threshold domain ranking.