I want to write a small applet for gnome3, any suggestions where to start?

So I have a service that works.
every 5 minutes the service is being tested and then there is a result
txt file.
I want to see in the applet bar of gnome3(top not buttom) near the
network status, a status for my service…
let say the network applet shows when there is a wire or wireless
network connection and the connection has IP address.

I want to test the network connectivity… like a http service
availability.
I would very like to have a list of tests that can be done on the fly
like DNS PING etc in a case of a problem.

any suggestions on where to start with that?
Also if there is an example I can see and understand I will be happy to
see.

Thanks,
Eliezer