I wrote this addon in the process of trying to debug another one.
Programmatically constructing a mesh, and keeping track of which
vertices to connect together into faces, became quite confusing, so I
decided it would be helpful if you could see the indices in the
various arrays displayed for the mesh directly in Blender’s 3D
viewport.

When installed and enabled, you will see a group of additional
checkboxes at the bottom of the Display panel in the Properties Shelf
at the side of the 3D viewport: “Show Verts”, “Show Edges”, “Show
Faces” and “Show Backface”. The first three control the display of
labels for vertices, edges and faces in the mesh respectively; the
last one controls where these are shown for faces oriented away from
the view. The display appears when a mesh object is active in both
Object and Edit modes.

Lawrence D'Oliveiro <ldo@geek-central.gen.nz>
2017 August 4