This extension is rendering a green button if the given DOM element available on the specified URL and red one when it is not.
The extension checks the given URL in the background periodically. It uses chrome's alarm API to do this so it does not consume to much resources. The frequency is around 1 request / minute. You can check for a specific element on the page too, doing this with the "elementToCheck" field, which accepts jQuery selectors. For example you can check the page http://www.bbc.co.uk/sport/0/football/ for having "Brighton" in the headlines. Where you should specify elementToCheck to div#more-new-headlines:contains(Brighton) . That is it. Enjoy using this tool!