Check against GRASS

[rsbivand]

Have you checked with a topological vector model GIS, like GRASS? Are the output polygons different with v.generalize?

[ateucher]

I haven't, but it would be interesting to see. It doesn't look like v.generalize has the option to use the Visvalingam simplification method, which is what mapshaper uses by default, so I'm guessing this will cause some differences.