1. A method comprising: extracting features from an application of a plurality of applications linked to an online system, the plurality of applications operate independently of and external to the online system, are used by users of the online system, and are configured to post content to the online system; applying a trained model to the extracted features of the application to generate a quality score for the application, the trained model is trained by: identifying a set of features from a set of training applications from the plurality of applications, and manually assigning quality scores to each of the set of features from the set of training applications, the manually assigned quality scores indicating whether each training application satisfies one or more of a set of criteria, and the trained model generates the quality score for the application based on the quality scores assigned to the set of features of the set of training applications, the generated quality score representing a probability of the application satisfying the set of criteria; ranking for presentation to a user of the online system, content provided by the application in relation to other content of the online system based on the generated quality score; and presenting the content provided by the application to the user of the online system according to the ranking.