What it Does
It reads your html and eliminates tags that are not part of the AnyBrowser specification. It then allows you to view this modified page in real time in your existing browser.

It does try to break your site. Web browsers are very forgiving of errors. Even if your pages work in every browser you've tried they can still be incorrect. Fixing your pages will help insure compatibility.

What it Does Not Do
It does not show how your browser will be rendered in various browsers or on different platforms. HTML does not specify how a page will look. There is no HTML rendering specification.

It does not check the syntax of your HTML. You should do this prior to using the site viewer. Use the HTML syntax checker for this.