Upload a GeoJSON or a Shapefile and check it for the five recurring topology errors — overlap, gap, sliver, duplicates, dangle. Free, runs entirely in your browser: the file never leaves your computer.
Upload a GeoJSON or a Shapefile and check whether every geometry is valid under the Simple Features model — with the reason for each error and an optional automatic repair you can download. Free, runs entirely in your browser: the file never leaves your computer.