Symfony2 comes with one built-in tool capable of making our life much easier. This tool is called the Web Debug Toolbar. The Web Debug Toolbar is the element sitting at the bottom of the page, and it gives you access to the full profiler page.

When you launch the to-do application, you should see a little Symfony2 icon on the right-bottom corner of the screen. Click on this icon. After you do this, you should see something similar to the following screenshot (without the first three sections):

The first section visible on this screen describes the controller used to display this page, action, and routing name. Also, it shows the status code returned by the controller. If you wish to have more detailed information, hover on the element (do not click on it yet).

The next section describes the AJAX requests passed to the controller. In the current state, there are no AJAX requests. We will try to create one later on.

The third visible section is a timer, that is, the total...