We introduce HexaLab: a WebGL application for real time visualization, exploration and assessment of hexahedral meshes. HexaLab can be used by simply opening www.hexalab.net. Our visualization tool targets both users and scholars. Practitioners who employ hexmeshes for Finite Element Analysis, can readily check mesh quality and assess its usability for simulation. Researchers involved in mesh generation may use HexaLab to perform a detailed analysis of the mesh structure, isolating weak points and testing new solutions to improve on the state of the art and generate high quality images. To this end, we support a wide variety of visualization and volume inspection tools. Our system offers also immediate access to a repository containing all the publicly available meshes produced with the most recent techniques for hexmesh generation. We believe HexaLab, providing a common tool for visualizing, assessing and distributing results, will push forward the recent strive for replicability in our scientific community. Figure 1: A screen-shot of HexaLab running inside Chrome under macOS. Model courtesy of [1]. Intended usagesVisualization: the main function of HexaLab is to serve as an advanced 3D visualizer for hex-meshes, for the purpose of providing a visual insight on the inspected models, and thus, indirectly, on the algorithms that produced them. The visualization of a hex-mesh is complicated by the resolution of the model and, even more so, by the presence of non-trivial 3D internal structures. HexaLab faces this task by offering a set of interactively controlled tools (cutting planes, etc), a shape-revealing realistic lighting (drastically improving the readability of images), novel modalities specifically designed to better communicate the shape of the cells, as well as colormaps and spatial glyphs, to reveal the quality, the topological characteristics, and so on. Assessment: for the same purpose, HexaLab can be used