Frontend tool events

When the agent calls a backend @frontend_tool (e.g. zoom_to, draw_geometry, show_toast), the step arrives with state: "frontend_tool" plus the event name and payload. Wire it to your map with onFrontendEvent:

<AgentChat
  apiBaseUrl="http://localhost:8000/api/v1"
  onFrontendEvent={(ev) => {
    switch (ev.event_name) {
      case "zoom_to":
        map.flyTo([ev.payload.lat, ev.payload.lon], ev.payload.zoom);
        break;
      case "draw_geometry":
        addGeoJSON(JSON.parse(ev.payload.geojson));
        break;
      case "show_toast":
        toast[ev.payload.level](ev.payload.message);
        break;
    }
  }}
/>;

type FrontendToolEvent = {
  event_name: string;
  payload: object;
  tool_name?: string;
};

Built-in GIS events

These six are pre-registered by the backend package (import stacgis_ai):

Event	Purpose	Typical payload
zoom_to	Navigate the map viewport to a coordinate	{ lat, lon, zoom }
highlight_feature	Highlight a feature by id	{ feature_id, layer_id }
show_toast	Display a toast notification	{ message, level } — level: info | success | warn | error
open_panel	Open a named side panel / drawer	{ panel_id }
draw_geometry	Draw a GeoJSON overlay	{ geojson, layer_id } — geojson is a JSON string
set_layer_visibility	Show / hide a map layer	{ layer_id, visible }

:::tip App-defined events The built-in set is a starting point — register anything else with @frontend_tool(event="…") on the backend. The frontend needs no changes to deliver new events, as long as you handle them in onFrontendEvent. The demo app defines two of its own: select_location (opens the map location picker, with an optional query prefill) and reset (resets the chat). :::

Define your own on the backend with the @frontend_tool decorator — the frontend needs no changes to render new events, as long as you handle them in onFrontendEvent.