Without a key the tool still works fully, using free OpenStreetMap data. With a key: address fields get Google's autocomplete (much better at matching exact shop/business locations), and you get a real embedded map with the route drawn on it. Get a key at console.cloud.google.com — enable Maps JavaScript API, Places API (New) (a separate product from the old "Places API" — search for it by that exact name), Distance Matrix API, and Geocoding API (used as a fallback when a field isn't picked from the dropdown — e.g. a pre-filled address). Since this tool doesn't run on your own domain, set the key's application restriction to None and instead restrict it by API restrictions to just those four APIs. Google's free monthly credit covers typical daily use for one team; the key is only used in your browser and isn't sent anywhere by this tool.