This paper considers the potential of web-analytic tools for a detailed study of the main fields of work of libraries in the web environment, study of user behavior, and analysis of the relevance of library information products and services offered on the sites. It presents the parameters for assessing the audience of library web resources (attendance, traffic sources, geography of users, etc.) using plug-ins, log-analyzers, counters, ratings, and services (Google Analytics, Yandex.Metrics, and Hotlog). The sites of several world libraries are analyzed by marketing tools (Hubspot Website Grader, Nibbler, CheckTrust, Google page-speed insights, and Hemingway)