This projects utilizes the great debug bar by maximebf.
It replaces the Contao internal debug bar entirely and provides several debugging inspections, all without the need to install any PHP extension or the like.
Add to your composer.json in the require section:
"cyberspectrum/contao-debugger": "~1.0"
Simply enable the Contao debug mode as usual and you are all set. You will see a small icon on the bottom left corner in the front and backend of Contao. Click on it and the debug bar will expand.