Libraries have had to reorient their activities and services due to the closure of their physical facilities during the Covid-19 crisis. In the framework of higher education, educational institutions have transferred their teaching and research to the online environment. University libraries have always been an essential element in the development of teaching and educational activities, and their role has been crucial during the confinement period. This research aims to analyze how Spanish university libraries have communicated this new way of providing their services through Twitter during the first weeks of the state of alarm. A total of 11,867 tweets and retweets from 56 libraries were analyzed based on an ad hoc thematic categorization. The conclusions highlight the role of libraries in the face of the health emergency and the transformation and publicity of this new way of working, as well as their role as an important information point to keep up to date with the current situation of the pandemic.