HTML5 outliner is a small tool that helps you check the outline of your HTML5 markup to get an overview of your document. Given the new contextual tags in the latest iteration of the markup language, it can sometimes get confusing to visualize the final outcome of your code.
That’s where the HTML5 outliner comes in handy. Simply paste in your code, point it to a URL or upload a file and it will give you an outline of what your site will look like. If you are a web designer / developer, the HTML5 outliner is yet another tool to have in your toolkit.