Follow the 5 W's:
Who:
Who is responsible for the creation of the site? Do they have listed credentials? Are they associated with a reputable institution?
What: What is the purpose of this site? What is the URL of the site and what might that tell you about its purpose?
Where: Where is this information coming from? Is there a bibliography or listed references? Is the site listed with an established institution?
When: When was the site last updated? Does the site even have a date? Does the currency of the information directly impact your subject?
Why: Why is this website useful for your research? Is it necessary for your research or could you find the information through a better source?