An analysis of the impact of Covid-19 on the use of Spanish university libraries during 2020 versus 2019 is carried out in this paper. The results have been published in a web tool that allows for deeper analysis of the individual libraries as well as the libraries as a whole. This study is not an evaluation of the libraries themselves but consists of measuring, describing, and quantifying the negative impact that the health crisis had on them during 2020. Visits, loans, user training, and catalog visits are variables that were strongly affected, with a significant positive increase being identified only in visits to library web pages. The use of digital resources according to Counter-compiled data increased considerably in some private university libraries, where possible staff cuts were also identified. The paper concludes by outlining reflections that can be further studied with the experiences of people related to libraries and with additional research, including data for the following years after collection and publication. [ABSTRACT FROM AUTHOR]