Background: Online Collaborative Writing (OCW) has been reported to be useful to improve writing quality in higher education. However, challenges emerge during the collaborative processes, mainly centering on how to sustain active interactions and communications in order to complete a high quality of writing. Objectives: Using the design-based research, this research designs and implements a student-facing SLA tool that integrates multi-method analytics to present social interactions, writing topics, and topic connections and to empirically investigate the effects of this tool on student engagement during OCW. Methods: This research uses both quantitative content analysis, statistical analysis, and qualitative analysis to examine the effects of the SLA tool on students' social and cognitive engagement as well as students' perceptions about the usefulness and usability of this tool. Results and Conclusions: Results showed that the SLA tool improved students' social and cognitive engagement, and most students perceived that the SLA tool was useful for the OCW activity. Based on the findings, implications of tool development and pedagogical design are proposed to foster students' online collaborative writing quality.