Show diagnostic workflow: "First thing I check is the Doctrine panel — if the query count is high, I have an N+1 problem. Then the Security panel if access control is behaving unexpectedly. The profiler is my first stop before any other debugging tool."
The debug toolbar shows: request info, response status, route, controller, database queries (count and time), memory usage, Twig renders, logged messages, and security context. Click to expand the full profiler with detailed panels. Key panels: Doctrine (every SQL query with parameters), Security (authenticated user and voter decisions), Events (dispatched events and listeners), and Mailer (sent emails). For production: use the profiler sparingly (enable for specific IPs), or use APM tools (Blackfire, Datadog). Strong candidates mention: using the Doctrine panel to spot N+1 queries, the Security panel to debug voter decisions, profiling specific requests by token, and that the profiler should never be enabled publicly in production.
Baseline Symfony debugging skill. Candidates who do not use the profiler are debugging blind. Those who can navigate the panels and extract actionable information debug efficiently.