Tsunami simulation software is essential in modern warning systems to characterize tsunami hazard, but its complexity discourages uses in risk management such as communication and public education. However, the ubiquity of web browsers and the appearance of web standards like WebGL that enable access to the Graphics Processing Unit (GPU), open the opportunity to reach other disciplines and communities. In this work, we developed an open source Javascript-WebGL library that enables users to run tsunami simulations that represent the propagation of long waves in the ocean efficiently on the web browser using the GPU. Through examples, it is demonstrated how Nami can produce results commonly seen in tsunami hazard assessment, and also other applications where the simulator is tightly integrated with other web elements, data sources and sensors. The latter is demonstrated with TsunamiLab, a web platform for public education and tsunami awareness developed with Nami at its core.