These tools will allow you to see what how the spiders see your site by emulating the spiders. Some Content and Links displayed on your webpage may not be visible to the Search Engines. For example, Flash based content, content generated through javascript, content displayed as images, etc... These tools emulate a Search Engine by displaying the html contents of a website page in the same way that a Search Engine would see it. They will also display the hyperlinks that would be crawled by a Search Engine when it visits your website.