Test GET API using Fiddler
Start Fiddler and make sure Fiddler is not capturing external traffic by clicking in the left bottom corner of the screen as shown below to keep this field empty. Select Composer tab and paste the GET API URL you want to to test, and send value through query string variable like below:
Click Execute button and watch how Fiddler traced its call. Select traced message on the left pane, Inspectors tab and Raw tabs for request (top right pane) and response (bottom right pane). Observe original request and received JSON response.