The Model Inspector allows you to study details about a model's geometry, topology, materials, and textures. Activate it by clicking/tapping the button in the bottom right of the viewer or pressing the I key.

You cannot disable the Inspector from the Sketchfab viewer. Users can always use the keyboard shortcuts described below to see the UI functions. However, if you're on a Premium plan or above and you'd like to hide the Inspector icon, as well as other UI elements, you can do so with the UI embed parameters.

You can toggle "Single Sided" to view only the front face of meshes. This is the same as the single sided rendering option in material settings.

The wireframe view lets you see the mesh's topology (triangles, quads, n-Gons). The keyboard shortcut is 5. If you'd like, you can choose a color from the Model Inspector menu.

You can choose between showing a 3D view of the model, a 2D view of the selected texture, or both side by side.

If you prefer not to allow your textures to be inspected directly, you can disable the 2D view in Model Properties.

When viewing 3D+2D, there will be feedback on your cursor showing the position in both views.

Final Render and No Post-Processing allow you to enable or disable Post-processing filters. The keyboard shortcut is 1.

You can inspect each material channel that's active on the model (base color, normal map, etc.). The keyboard shortcut is 2.

If you're using 3D+2D or 2D mode and the model has more than one material, you can choose a material in the scene by clicking/tapping it in the viewer or from the drop-down menu in the top-right. If a model has more than one UV set, you can also switch between them from the drop-down menu.

You can enable MatCap mode and MatCap + Surface (if the material has a normal map), as well as show the blank Geometry to better inspect the wireframe, and display vertex normals. The keyboard shortcut to toggle through them is 3 but you can combine the views together with MatCap (3) and Wireframe (5).

The UV Checker lets you inspect the model's UVs using a sample grid texture. The UV Checker is only available if the model uses a texture. The keyboard shortcut is 4.

If you would like to use this UV checker image in your own projects, you can download it here.

You can view Bones and Bone Weights in animated, rigged models. The keyboard shortcut is 6.

There are some caveats: First, of course, the model needs to contain some form of bone-driven armature. Remember that many animations on Sketchfab use simple scale, rotation, and translation, as well as morph target animations, which work without bones. Second, some bone placements are approximated. This is the nature of how common file formats such as FBX store animation data and is not a limitation of Sketchfab. If you need specific information, you can always leave a comment on a model you're interested in to learn or see more from the contributor.