REST API within later versions of WordPress will provide the possibility of being able to use the second version of the infrastructure of the API that is now a part of the core in WordPress. The activation will lead to a REST API for the content of your site and will expose your data in a JSON format. The response data that you will receive is going to be similar to what you would get in the WordPress loop, with the sole difference being the format, which is JSON, which will allow display in any way, and can even filter the API calls in a similar manner to the loop.
We shall assess the fact that some API calls are going to require authentication and, just like WordPress required authentication to get access to
wp-admin or to create a new post, most GET requests will not require authentication and will allow content to be displayed via the API to a third-party external app without requiring a credentials request for the user.
WordPress is the content...