G'MIC stores in a zlib compressed format its list of filter parameters, with enough details that GUIs can be built to expose and manipulate them. So far, each application implementing G'MIC with a user interface would either gmic-qt which has its own parser or write their own parser for those parameters.
In order to design webservices or different types of UIs on top of G'MIC (in the case of gmic-blender, compositing/texture nodes), the JSON output format for this parser can come in pretty handy!! One little issue is that the result is long to get, so the JSON file should be generated once for all and possibly embedded in your application, with a per-release refresh.
This json file is stored online on gmic.eu at the url http://gmic.eu/update290.json (or 291 etc.. for further G'MIC releases), with possible in-the-hour update, following the contributions on new/updated community gmic filters in the gmic-community Github repository's include directory.