The Endpoints APIs Explorer has moved

The Endpoints APIs Explorer has moved to be part of Cloud Endpoints Portals.

Cloud Endpoints Portals can be set up for any Google Cloud Endpoints API. These portals generate documentation for your API(s), with an interactive exploration tool alongside just like the previous APIs Explorer.

Check out the getting started page to set up your own portal. Make sure you complete the "Added API management" prerequisite step if you haven't already, since this isn't done by default for Endpoints Frameworks.