In an older article I introduced a tool called Wired Marker. It basically allows you to mark text on a website. As it is tedious to mark all the words, you can use your Anki decks, use the export feature, limit it to vocabulary, and export them to text files. Import the files one after the other, and remove the tags that Anki has added. Preferably you should do this with Excel, as you will need one word or sentence per line, for later use in Wired Marker.
Once all the tags are removed, you should save the file in .utf8 format, and start Firefox. Activate Wired Marker, right click on the color of the marker you prefer, and click on Auto Marking, Dictionary, Read in the dictionary … Now you are supposed to select your text file containing your words and sentences. It will take some seconds until Wired Marker has read the file in so be patient. After the process has finished, click on the Marker, Auto Marker, Dictionary, Manage dictionary to see that all the words and sentences are there.
As soon as this is done and everything went alright, you can visit any website, right click on the Marker, Auto marking, Dictionary, and Apply the dictionary. Wired Marker will check the website content against the content of your dictionary, and mark all the words you should know for you. This can take quite a while, depending on the number of your entries, so again be a little patient.
By doing this, it is easy to see how much you know, and to spot all the unknown items in a text. So you should be able to determine how easy or hard it is, to read the text on a website as a whole.