Can google chrome extensions monitor page activity?

I was wondering if chrome extensions can monitor page activity.
I'm making a tool that would make my life a lot easier if GC extensions could monitor page activity.

When I'm in a forum, I want to be able to type "my twitter" and the GC extension automatically prepend and append and (http://twitter.com/shamelessplug).

Thanks for any help.
I know extensions can monitor what page you're on. the google plus extension does it.

I know that the Silver bird twitter extension also reaches out for data even when you haven't clicked on it.

Thanks for any help!