FoldSpy is a graphical tool to respond the very easy question- which part of your web page is fold over i.e. able to be seen without scrolling. Since you know, this is a query without a compact answer, because different users use different browsers and screen resolutions, run different toolbars, and so on. After entered in the service, you insert a single line of javascript in your page header and then open your web page using a #foldspy anchor. You will see a status bar and gradient overlay to demonstrate what percentage of users can see the each part of the web page.

YSlow come up to the Yahoo's Developer Network. This is attached to the Firebug plug-in for Firefox inform you why your web pages are slow. It examines the whole thing from the size of components to gzipped, ETags be configured, and JavaScript is well minified, and then provide you a report with suggestion for improving performance. Not every suggestion will be relevant to every site, but if you select and choose you can get areas wherever a small work will result in a big improvement.