Basic API endpoints to get ClassicPress up and running: https://api-v1.classicpress.net/
Ensure you are using at least PHP 7.0, and run:
php -S localhost:8000 router-v1.php
You can then visit http://localhost:8000/ in a browser.
Note that some endpoints respond differently depending on whether they are
requested by a browser or another client, based on whether the Accept header
contains text/html.