You are browsing the Symfony 4.1 documentation, which changes significantly from Symfony 3.x. If your app doesn't use Symfony 4.1 yet, browse the Symfony 3.4 documentation.
The profiler is a powerful development tool that gives detailed information about the execution of any request.
Never enable the profiler in production environments as it will lead to major security vulnerabilities in your project.
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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