The material is well-written, well-researched and relevant.
Does the webpage have spelling or grammatical errors? Is the site easily navigable? Does the site look professional? Is it useful? Is it relevant to my needs?
The information can be verified using another source. If I look at another web site, book, or article on the same topic, I can find the same facts used on this site.
Can I find the same facts repeated in different sources?
The information is up-to-date. (If the site does not tell you when the information was updated, how will you know?)
Is the information the latest available on the topic?
Here are two web pages on sleep:
Notice the differences in content between these two pages:
One of these pages has references; these are the sources the author used to write this page.
The other does not.
The references provided by the Sleep and Memory page allow you to read the original studies and check the author's facts.
Since the other page does not provide references it is more difficult to verify the information given. What are these studies the author refers to? To check the consistency of this page, we need to google some of the facts listed and see whether another web site will tell us the same thing. We could also look at a book or a magazine article. If you are researching a topic you will usually look at multiple sources; see whether they agree on the facts.
Look for dates on each of the above pages. Now think about whether you need the most up-to-date information for this topic.