Convert GeoJSON to GPX

A route built in a web map, exported from QGIS, or generated with a script usually comes out as GeoJSON — a LineString with a coordinateProperties block carrying your timestamps and sensor readings. That's a natural shape for Leaflet or Mapbox, but a Garmin head unit, a Wahoo, or Strava's upload form won't touch it; they want GPX. This tool reads the geometry and the coordinateProperties arrays together and writes a standard GPX track, one trkpt per coordinate, so the file opens on essentially any GPS device or fitness platform in existence — GPX is the closest thing this space has to a universal format, and it's the safest target when you don't know exactly what will open the file next. Position, elevation, and timestamps carry over exactly, and heart rate and cadence transfer cleanly into GPX's extension schema. Two things don't survive the trip, not because of a bug but because GPX itself has no place for them: distance and speed are dropped, since GPX never defines fields for either, and power is downgraded, carried in a vendor extension that some older tools ignore rather than a first-class field. If your source GeoJSON has no sensor data at all — just a plain route with coordinates — you'll get a clean track-only GPX, which is exactly what most navigation apps expect anyway. Everything happens locally: the parsing, the unit conversion, the XML writing, all in a background worker in your browser, so a route with hundreds of thousands of points doesn't freeze the tab, and the file itself never touches a server.