The ressources, that are returned by the API, line real estate objects, short list entries, saved searches, will expire , so we discourage caching on the client side. To minimize response time and network traffic the API supports HTTP Etags and datestamps. If your network library has Etag and datestamp support, we recommend using If-None-Match- or If-Modified-Since-Headers. If one of the clients Etag matches the resource on the server or the resource was not updated since the last request, it will send an empty reply with a 304 Not Modified status. If you have both options of using If-None-Match or If-Modified-Since, we recommend using If-None-Match (Etags).