This is a really simple webhook implementation that gets Api.ai classification JSON (i.e. a JSON output of Api.ai /query endpoint) and returns a fulfillment response.
More info about Api.ai webhooks could be found here: Api.ai Webhook
It's a weather information fulfillment service that uses Yahoo! Weather API.
The services takes the geo-city parameter from the action, performs geolocation for the city and requests weather information from Yahoo! Weather public API.
The service packs the result in the Api.ai webhook-compatible response JSON and returns it to Api.ai.