How to generate class diagram from project in Visual Studio 2013?

For creating real UML class diagrams:

In Visual Studio 2013 Ultimate you can do this without any external tools.

• In the menu, click on Architecture, New Diagram Select UML Class Diagram
• This will ask you to create a new Modeling Project if you don't have one already.

You will have a empty UMLClassDiagram.classdiagram.

• Again, go to Architecture, Windows, Architecture Explorer.
• A window will pop up with your namespaces, Choose Class View.
• Then a list of sub-namespaces will appear, if any. Choose one, select the classes and drag them to the empty UMLClassDiagram1.classdiagram window.

Reference: Create UML Class Diagrams from Code

Right click on the project in solution explorer or class view window --> "View" --> "View Class Diagram"