Digital transformation accelerates the undertaking of online learning at various levels of education. Online learning mandates students to have high self-regulation skills. Therefore, self-regulated learning (SRL) plays an important role in the education field. In the third wave of SRL measurements, there is an idea of how measurement is applied concurrently with the intervention. This study proposes a learning diary that we call Diaria to take part in the third wave. Diaria was developed by means of the user-centred design with three phases, including design research, design prototype, and design evaluation. Usability testing was selected as an evaluation design method involving 30 participants. The evaluation results were examined based on several categories, including distribution of the System Usability Scale score, issues category, task performance, and potential solution. An initial investigation of the impact of learning diaries on students' SRL skills was carried out as a pilot study. This experiment involved 24 participants in a linear algebra course. The interview method was applied to collect data, followed by thematic content analysis to understand the resulting transcripts. The findings exhibited the prototype has good usability. In addition, recommendations for improvement are suggested. Meanwhile, the pilot study shows that there are various student learning strategies, advantages to a learning diary, and several valuable notes for the main study.