This paper investigates the influence of news agency Algemeen Nederlands Persbureau (ANP) on the coverage and diversity of political news in Dutch national newspapers. Using computational text analysis, we analyzed the influence on print newspapers across three years (1996, 2008, and 2013) and compared influence on print and online newspapers in 2013. Results indicate that the influence of ANP on print newspapers only increased slightly. Online newspapers, however, depend heavily on ANP and are highly similar as a result of such dependence. We draw conclusions relating to the gatekeeping role of news agencies in the digital age in general, and in the context of the Netherlands in particular. Additionally, we demonstrate that techniques from the field of information retrieval can be used to perform these analyses on a large scale. Our scripts and instructions are published open-source to stimulate the use of these techniques in communication studies.