Normal 0 21 false false false DE X-NONE X-NONE Most altmetric studies compare how often a publication has been cited or mentioned on the Web. Yet, a closer look at altmetric analyses reveals that the altmetric tools employed and the social media platforms considered may have a significant effect on the available information and ensuing interpretation. Therefore, it is indicated to investigate and compare the various tools currently available for altmetric analyses and the social media platforms they draw upon. This paper will present results from a comparative altmetric analysis conducted employing four well-established altmetric services based on a broad, multidisciplinary sample of scientific publications. Our study reveals that for several data sources the coverage of findable publications on social media platforms and metric counts (impact) can vary across altmetric data providers.