Sometimes we have written a good program that compiles nicely. We build the project, run the server, and navigate to our app. At some point while navigating through our pages, we get an error and a page isn't returned. This generally results in a 500 server error message in the browser. (We'll cover server messages later.) Unfortunately, this vague message isn't helpful for debugging our code.

In Startup.cs, we can add a service that will provide a more detailed error message when a Razor page fails to load due to a server error. Within the Configure() method - the same method that declares app.UseMvc() - add a new line of code:

...
    public void Configure(IApplicationBuilder app)
    {
        app.UseDeveloperExceptionPage();  //This is the new line of code
        ...

This will produce a friendly error report when Razor fails to load.