This article discusses the development of an interactive online textbook for undergraduate teaching, in response to moving teaching online due to COVID-19. The development took place initially for a university with less than 5% of students studying online in 2019. The online textbook was incorporated into a large, diverse, multidisciplinary and predominantly first-year undergraduate research design and statistics course. Digital tools were embedded into the textbook to facilitate student engagement in lieu of face-to-face contact, including online crosswords for low-level statistical literacy, drop-and-drag activities, screencasts, exercises, animations, and videos. The textbook was prepared in markdown format. This approach allows for instant updating of material and provides focussed URLs that educators can use to point students directly to specific learning outcomes. Despite the textbook being developed in response to restricted teaching conditions, it has provided a cost-effective resource, targeted at teaching research design and basic statistics concepts, interpretation, and communication. Having returned to face-to-face teaching, the text is now fully integrated into the course. Importantly, the online textbook is freely available for other educators to use, either in its existing form, or by forking (on Github) the textbook sources to create a bespoke online textbook for other courses.