Symfony2 comes with the Web Profiler, a plugin that allows a developer to check how their application is performing. The Web Profiler collects information about each request made to the site and allows you to visualize it within the browser. The Web Profiler bundle isn't included in Drupal 8 by default but it can be installed as part of the Devel module.
Using the Web Profiler
Installing the Web Profiler module
The Web Profiler module is a submodule of the Devel module. When you download the Devel module, it becomes available and you can enable it either through the user interface or by running drush pm-enable webprofiler. There are some additional configuration steps you need to perform in order to use all of the functionality...