Solid Inspector in SketchUp for Web
Solid Inspector in SketchUp for Web helps you find and fix problems that prevent SketchUp from classifying geometry in your model as a solid. Making sure entities are solids can help when exporting to formats suitable for 3D printing, and is necessary when using some SketchUp tools.
Using Solid Inspector
Solid Inspector appears at the bottom of the panels on the right-hand side of the SketchUp for Web interface.

When activated, the tool asks you to select a group or component. If your selection isn’t a group or component, the tool won’t work. After selecting an entity, click Run Inspection. Solid Inspector will list any issues it finds and highlight where they are in your model in red.

Solid Inspector can automatically fix the following errors:
Reversed faces
Stray edges
Holes in a face
Some errors can’t be fixed automatically. These errors require you to manually edit your model:
Border holes
Nested groups/components
Image entities
Short edges
Each error appears listed in the Solid Inspector panel. Selecting an error zooms to the error’s location.