Perusall, a web-based collaborative reading platform characterised by its social annotation functionalities, was introduced in a postgraduate teacher-training language-awareness course in Hong Kong during the shift to online teaching and learning brought about by the global COVID-19 pandemic. Tasks were designed on Perusall to engage the participants in reading the literature and references on grammar and lexis teaching and in analyses of coursebook materials and classroom-teaching excerpts. In this article, I discuss why Perusall was adopted, the pedagogic innovations at different stages, the impact this had on sharpening participants' teacher language awareness, and the implications this has for both teacher education and language learning. I aim to highlight how autonomy can be fostered via effective task design and student-centred pedagogies. I maintain that it is not just the platform that matters but how Perusall is utilised with a strategic blend of synchronous and asynchronous classroom activities and instructor intervention to promote teacher language-awareness gains and the empowerment of teachers as grammar specialists and critical coursebook analysts and users.