The pages json plugin for Grav provides a very basic json api for accessing pages from Grav.
Download and unpack a zip (or clone this repository) into the user/plugins directory of your project
Simply copy the user/plugins/grav-plugin-pages-json/grav-plugin-pages-json.yaml into user/config/grav-plugin-pages-json/grav-plugin-pages-json.yaml and make your modifications.
enabled: true
Send a request to any page on your site with the Accept header set to application/json and the plugin will return the response in a json structure.