It sounds pretty good. A couple of suggestions..."To get a grasp of the validity of the content" might sound better to say "To understand the content." I'm not sure what the purpose of this sentence might be since it is self made but it might be easier to read with bullet points, such as:
To get a grasp of the validity of the content, there are five evaluation guidelines to check for:
*Accuracy—are sources of information available for cross-checking?
*Authority—who wrote the page and do they a proper credentials to present the information?
Otherwise, it just appears as a really long, run on sentence.
Student or Learner