This app is a REST-based server created to echo the request input back to the calling application.
Once running in a web server, execute a GET command of the following form: <path-to-server>/echo?value=<your-echo-value-here>. The response body should contain only the value you sent.
There is also a JSON-based implementation. Use a URL of the form: <path-to-server>/echo/json?value=<your-echo-value-here>. It will return a JSON representation of the value posted.