We are looking for rest API URL to get application health which shows if application is in critical , warning or normal.
Any help is appreaciated.
Are you asking if you can create an API call from within AppD to go elsewhere? If so, then I think you can create health rules which trigger an HTTP request, which can POST to wherever you want.
One of these links might help:
https://docs.appdynamics.com/display/PRO45/Metric+and+Snapshot+API#MetricandSnapshotAPI-RetrieveMetr...
or
https://docs.appdynamics.com/display/PRO45/HTTP+Request+Actions+and+Templates
