Dev question -- Bowser Extensions -- Expert wanted

Hi.

For the serious expert browser extension developers out here.

Is there a way of creating an extension that would allow me to "monitor" check on Saas apps -- or a given target baseURL.

I've seen reference to a numer of different "Subscription Monitoring Apps" and was wondering if these apps are desktop only, mobile only, or URL as well.

thanks for any input/pointers...