Abstract: This work shows the user experience (UX) assessment of a web-based platform for the semi-automatic usability evaluation of websites, UTAssistant, which is primarily addressed to workers in public administration (PA). The study is part (Phase 1) of a multiple assessment methodology which consists of four phases in total: (1) UX in laboratory conditions; (2) Usability evaluation in remote online conditions; (3) Usability evaluation in workplace conditions; and (4) Heuristic evaluation. In Phase 1, a UX study in laboratory conditions was carried out. Participants’ UX of a PA website navigation through UTAssistant was evaluated by both traditional self-report usability assessment tools (SUS and UMUX) and biobehavioral measurement techniques (facial expression recognition and electroencephalography). Results showed that using the UTAssistant usability assessment tool for webpages did not affect users’ perceived usability in terms of self-reports and affective states, which were mostly neutral for all the assessment session. However, frontal alpha asymmetry EEG’s scores showed a higher sensitivity of UTAssistant users to the duration of the trial, with a decrease in motivation displayed as the trial ensued. However, this result did not seem to affect emotional experience.