The User Interface (UI) is the first artefact that the user interacts with while developing a sense of trust that motivates him to use software applications more effectively. A badly designed UI can deceive users and bring the system into disrepute. Trustworthiness in UI is mandatory, as a poorly implemented UI can lead to the user misusing the system and jeopardizing the expected result. Trust in computational systems involves not only technical aspects, such as computational infrastructure, storage space, and service composition, but also aspects of Human-Computer Interaction (HCI). While technological aspects have received considerable attention, there are few research on human-computer interaction in terms of trust. This paper describes a way for assessing a system’s trustworthiness based on the user’s perception. The approach relies on a quality model to aggregate interface quality criteria in order to get a trustworthiness score. Three sets of experiments involving more than 300 individuals were carried out to validate the suggested methodology. A comparison was made between the trustworthiness score obtained through the methodology and the answers to open questions obtained through the users’ questionnaires. The results were consistent, and statistical analysis corroborated the positive assessment. Based on these results, examples of improvements were developed to highlight the usefulness of the approach for developing more trustworthiness interfaces.