I use React DevTools to inspect components and state, the Profiler for performance, the Network tab for API issues, read the console, use strategic logs and binary search to narrow the cause, and isolate hard bugs in a minimal example.

I measure with the Profiler first, then stabilize references with useCallback and useMemo, wrap re-rendering components with React.memo, virtualize long lists, lazy-load images, code split routes, and debounce expensive inputs. I measure again to confirm each fix helps.

Use semantic HTML, give interactive elements accessible names, ensure keyboard accessibility, manage focus for modals and menus, ensure sufficient color contrast, use ARIA only when needed, and test with a screen reader.