Many information retrieval tasks require viewing documents in some manner, whether this is to view information in context or to provide annotations for some downstream task (e.g., evaluation or system training). Building a high-quality document viewer often exceeds the resources of many researchers and so, in this paper, we describe the design and architecture of our new open-source document viewer, Spectator. In particular, we provide a look into the algorithmic details of how Spectator accomplishes tasks like mapping annotations back to the canonical document. Moreover, we provide a sampling of the use cases that we envision for Spectator, potential future additions depending on community need and support, and highlight situations where Spectator may not be a good fit. Furthermore, we provide a brief description of the sample application that we bundle with Spectator to demonstrate how one might use it within the context of a larger system.