Every Drupal site has a status report dashboard at /admin/reports/status. This module allows you to expose, as JSON, whether everything is OK or not.
The idea is that if you are managing several Drupal sites, you can set up a dashboard or some Jenkins jobs to keep track of the status of all sites in one place.
Typical usage
(1) install and enable this module.
(2) get the token by running this on the command line: