The purpose of the article is to study public communications in digital platforms of public administration in Russia. In recent years, there has been an intensive introduction of digital platforms into the practice of public administration, and communications within the platforms have become part of the national system of public communications. The object of research in this article will be public communications in two digital platforms in Russia: St. Petersburg and the Leningrad region. In the period from December 1, 2019 to November 1, 2020, we collected 10993 messages from the Our St. Petersburg platform and 3758 messages from the People's Expertise platform. The main research methods were the Text Mining method and qualitative analysis of messages. The results of the study of the platforms «Our St. Petersburg» and «People's Expertise» show that the practice of communication in them is very different from the ideals of public democratic communication. The most characteristic differences are the problematic nature of communications: citizens turn to authorities to solve problems most often in the field of housing and communal services. Public communications in the studied urban communication platforms are very different from communications in social networks in their limitations; platform affordances inhibit the spread of discussions. The most important epistemic authority in public communications is bureaucratic rules and appeals to legal procedures. When analyzing the procedure of political reasoning on digital platforms, some methods of manipulative presentation of information are revealed.