You are browsing the Symfony 4.0 documentation, which changes significantly from Symfony 3.x. If your app doesn't use Symfony 4.0 yet, browse the Symfony 3.4 documentation.
Symfony provides a powerful profiler to get detailed information about the execution of any request.
In applications using Symfony Flex, run this command to install the profiler before using it:
$ composer require --dev symfony/profiler-pack
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