Small stories research has recently been extended as a paradigm for interrogating the current storytelling boom on social media, which includes the design of stories as specific features on a range of platforms. This algorithmic engineering of stories has led to the hugely popular feature of Stories on Snapchat and Instagram (also Facebook and Weibo). This article offers a methodology for studying such designed stories, underpinned by a technographic, corpus-assisted narrative analysis that tracks media affordances, including platforms’ directives to users for how to tell stories and what stories to tell, discourses about stories as platformed features, and communicative practices. The article specifically focuses on the directive of authenticity in the storytellers’ self-presentation with data from influencers’ Instagram Stories. Authenticity is attestable in the values underlying the design of stories, the affordances offered, and the storytelling practices that these commonly lead to. The article singles out three constituents of authenticity vis-à-vis each of the above: the design of stories as vehicles for “imperfect sharing” and an amateur aesthetic; visual and textual affordances for sharing life-in-the moment; and the deployment of specific genres of small stories that anchor the tellings onto the here and now. These enregister a type of teller who offers a believable account of themselves and their life through affording an eyewitnessing quality to their audiences and access to their everyday.