Geocoding is a fundamental task of Geographic Information System (GIS) processing and analysis. It allows the transformation between a location reference (i.e., an address or an alphanumeric code) and coordinates, which is often an essential step when performing spatial analysis, mapping, and other geolocation related processes. Providing software functionality through RESTful APIs is a common practice in geospatial applications. Client programs are able to access or process geospatial data easily through a lightweight and scalable RESTful web service. Existing geocoding RESTful API providers include Google Maps Geocoding API, ArcGIS Geocoding REST API, MapQuest Open Geocoding API and what3words (w3w) Geocoding API. Extensions of what3words geocoding system have recently been proposed to overcome its limitation of fixed resolution and lack of consideration of the third dimension. This paper considers one of the extensions, the Quadtree Extension Model (QTEM) and introduces a RESTful API that provides operations for forward geocoding, reverse geocoding, single line and polygon encoding, and centre points encoding for a given area. The resources published by the web service could be implemented by software programs performing indoor and outdoor location referencing, location marking and path finding. This API could facilitate various geographic applications such as facility management, emergency evacuation, navigation and student survey data management in a university campus environment.