This bookmarklet highlights a lot of typical semantic HTML elements, conveying their tag names. This makes inspection of the current page's semantic structure pretty easy.
Go to bookmarklet.html and get the bookmarklet there.
Activate the bookmarklet by clicking on it. Then inspect the displayed results and make sure the used tags are semantically meaningful.
This is a slightly enriched version of the bookmarklet Inhalte gegliedert. Our version highlights some more elements like lists, tables, links, and forms.