Weather Server

Instructions

Args:
    city_name: Name of the city (e.g., "San Francisco", "New York", "Chicago")

Implementation Reference

• weather.py:193-227 (handler)

  The core handler function for the 'get_forecast_by_city' tool. Decorated with @mcp.tool() for automatic registration and schema generation from signature and docstring. Geocodes the city name, retrieves forecast data using helper functions, and returns a formatted string with forecast details for up to 10 periods.

  @mcp.tool()
  async def get_forecast_by_city(city_name: str) -> str:
      """Get weather forecast for a city by name.
  
      Args:
          city_name: Name of the city (e.g., "San Francisco", "New York", "Chicago")
      """
      coords = await geocode_location(city_name)
      
      if not coords:
          return f"Error: Could not find coordinates for '{city_name}'. Please check the city name and try again."
      
      latitude, longitude = coords
      forecast_data = await get_forecast_data(latitude, longitude)
      
      if not forecast_data:
          return f"Unable to fetch forecast data for {city_name}. The location may be outside NWS coverage area (US only)."
  
      periods = forecast_data["properties"]["periods"]
      location = forecast_data.get("_location", {})
      location_str = f"{location.get('city', city_name)}, {location.get('state', 'Unknown')}"
      
      forecasts = []
      for period in periods[:10]:
          forecast = f"""
  {period['name']}:
    Temperature: {period['temperature']}°{period['temperatureUnit']}
    Wind: {period['windSpeed']} {period['windDirection']}
    {f"Humidity: {period.get('relativeHumidity', {}).get('value', 'N/A')}%" if period.get('relativeHumidity') else ""}
    {f"Precipitation: {period.get('probabilityOfPrecipitation', {}).get('value', 0)}%" if period.get('probabilityOfPrecipitation') else ""}
    Forecast: {period['detailedForecast']}
  """
          forecasts.append(forecast)
  
      return f"Weather Forecast for {location_str}:\n" + "\n---\n".join(forecasts)

• weather.py:33-71 (helper)

  Helper function used by get_forecast_by_city to convert city name to latitude/longitude coordinates, prioritizing US locations using Open-Meteo geocoding API.

  async def geocode_location(city_name: str) -> tuple[float, float] | None:
      """Geocode a city name to latitude and longitude coordinates.
      
      Returns:
          Tuple of (latitude, longitude) or None if geocoding fails
      """
      async with httpx.AsyncClient() as client:
          try:
              # Try to get US results first by adding country code
              # Open-Meteo supports country_code parameter
              params = {
                  "name": city_name,
                  "count": 10,  # Get more results to find US cities
                  "language": "en",
                  "format": "json"
              }
              response = await client.get(
                  GEOCODE_API_BASE,
                  params=params,
                  timeout=10.0
              )
              response.raise_for_status()
              data = response.json()
              
              if data.get("results") and len(data["results"]) > 0:
                  # Prefer US results (country_code == "US")
                  for result in data["results"]:
                      if result.get("country_code") == "US":
                          return (result["latitude"], result["longitude"])
                  # If no US result found, return the first result anyway
                  # (user might be looking for a non-US city, or it might still work)
                  result = data["results"][0]
                  return (result["latitude"], result["longitude"])
              return None
          except httpx.RequestError:
              return None
          except Exception:
              return None

• weather.py:129-155 (helper)

  Helper function called by get_forecast_by_city to fetch detailed forecast data from the National Weather Service (NWS) API for given coordinates, including location metadata.

  async def get_forecast_data(latitude: float, longitude: float) -> dict[str, Any] | None:
      """Get forecast data for coordinates. Returns None on error."""
      if not validate_coordinates(latitude, longitude):
          return None
      
      points_url = f"{NWS_API_BASE}/points/{latitude},{longitude}"
      points_data = await make_nws_request(points_url)
  
      if not points_data or "properties" not in points_data:
          return None
  
      forecast_url = points_data["properties"].get("forecast")
      if not forecast_url:
          return None
  
      forecast_data = await make_nws_request(forecast_url)
      if not forecast_data or "properties" not in forecast_data:
          return None
  
      # Add location info to the forecast data
      location_info = points_data["properties"].get("relativeLocation", {})
      forecast_data["_location"] = {
          "city": location_info.get("properties", {}).get("city", "Unknown"),
          "state": location_info.get("properties", {}).get("state", "Unknown")
      }
      
      return forecast_data

• weather.py:28-31 (helper)

  Utility helper for validating latitude and longitude coordinates used indirectly in forecast retrieval.

  def validate_coordinates(latitude: float, longitude: float) -> bool:
      """Validate that coordinates are within valid ranges."""
      return -90 <= latitude <= 90 and -180 <= longitude <= 180