This report describes the specification of ErgoManager as well as the results from the first validation study associated with the development of this UIMS (User Interface Management System) intended to support webmasters at assuring "in use" quality for interactive Web sites. The ErgoManager UIMS aggregates two basic components: ErgoMonitor and ErgoCoIn. ErgoMonitor is a monitoring tool intended to quantify the "average" usability that web sites have been offering to theirs users. It applies task-oriented analysis as a way to identify specific instances of users' behaviors while they are accomplishing transactional tasks with the web site. In the sequence, ErgoMonitor determine the incidence and the duration of these behaviors and use these data to produce usability measures, which quantify the average productivity of interactions. ErgoCoIn is a checklist based CSEE (Computer Supported Ergonomic Evaluation) tool that features automatic services aimed at inquiring context of use aspects and recognizing web page components as a way to tailor focused ergonomic checklists. By integrating these tools, ErgoManager intends to support a quality assurance strategy based on the confrontation between usability quantitative metrics and qualitative aspects of user interfaces.