If you build web maps, sooner or later a KML file lands on your desk. KML was designed for Google Earth: XML-based, verbose, and great at storing styles and descriptions. Web mapping libraries like Leaflet, Mapbox GL JS, and OpenLayers, on the other hand, speak GeoJSON natively. Converting KML to GeoJSON is therefore one of the most common format chores in web cartography, and doing it well means understanding which method fits your situation rather than just hunting for the first online converter.

The easiest method requires no coding at all. Open QGIS, drag your KML file onto the map canvas, then right-click the layer and choose Export, then Save Features As. In the dialog, set the format to GeoJSON, pick a file name, and confirm the coordinate reference system. This works well when you already have the file in a desktop workflow — for example after turning spreadsheet coordinates into map layers, which follows a similar import-then-export routine.

For developers and anyone automating a pipeline, GDAL's ogr2ogr is the professional choice. A single terminal command — ogr2ogr -f GeoJSON output.geojson input.kml — converts the file, and GDAL handles the XML parsing, geometry translation, and attribute transfer for you. Because it runs from the command line, you can wrap it in a script and batch-convert hundreds of KML exports from field teams or partner agencies without opening any software.

If you need to inspect and clean the data during conversion, Mapshaper (mapshaper.org) is worth knowing. It runs entirely in your browser, lets you see the geometry, simplify overly detailed polygons to shrink file size, and then export as GeoJSON. For in-app conversion, the open-source togeojson JavaScript library parses KML in the browser so users can upload files directly to your web map without a server round-trip.

A few pitfalls catch people out. First, KML coordinates are always in WGS84 latitude/longitude, so confirm your output CRS before mixing the GeoJSON with other layers. Second, KML styling — colors, icons, balloon text — does not survive the trip to GeoJSON in any standard way, so plan to re-style with your web library. Third, KML files from Google Earth can be enormous; consider simplifying geometry before publishing, because a multi-megabyte GeoJSON will make your web map sluggish.

Once converted, validate the GeoJSON before it goes live. Load it into a fresh QGIS project or a simple Leaflet page over an OpenStreetMap basemap and check that every feature lands where it should. A quick visual check catches the classic errors: flipped coordinates, missing attributes, and empty geometries. With a verified file in hand, you can serve it statically, drop it into a tile pipeline, or feed it straight into your front-end map code.