Chrome Extension

We are looking for a very simple Chrome Extension that we can then build on. When an html page has loaded the extension should look for a certain peice of data (similar to the Google sample Page Action by Content) then it should pass the data it found to a server and that should return some JSON data and this should be injected into the current page. e.g. if we have this in the html <a href="mail:">Send email to Fred</a> we want to seach for href="mail: and then send the "" to a server which will return some JSON data about fred we then want to inject a DIV into the page after the </a> so it will show some additional data about Fred. The server code can be a simple PHP or similar file that returns hardcoded JSON data.