Kinematic analysis studies characterize human motion in healthy, pathologic, and rehabilitated subjects. These studies provide rich datasets which enable clinicians and researchers to understand disease progression, and the effects of surgical intervention and physical therapy. A variety of techniques - ranging from optical skin marker tracking to biplane fluoroscopy - are utilized to collect these datasets. The quantification and physical interpretation of these motion capture datasets (i.e. kinematic analysis) are predominantly conducted using Euler/Cardan angles (Diebel, 2006; Wikipedia, 2021; Zatsiorsky, 1998), whose output - time series of 3 angles - is presented in peer-reviewed manuscripts in 2D graphs (Ludewig et al., 2009). This rudimentary presentation, however, obscures the physical meaning behind Euler/Cardan analysis. As other authors have noted, the visualization of these angles enables meaningful discussion between biomechanics researchers and clinicians (Baker, 2011). A ubiquitous open-source method to concurrently visualize recorded human motion and the results of kinematic analysis is presently lacking in the biomechanics community. 'Kinematics-vis' is a JavaScript web application that visualizes kinematic analysis output resulting from motion capture studies.