Which two Flipper plugins diagnose an unresponsive UI?

WHAT THIS TESTS: A methodical approach to UI jank using measurement tools instead of intuition, and knowing what each tool actually reveals.

A GOOD ANSWER COVERS: Two complementary plugins. First, the React DevTools profiler integrated in Flipper records render commits, so you look for components with long render times, high re-render counts, or work done in render that should be memoized. Second, a performance and thread tool, the Performance plugin or Hermes sampling profiler, where you watch JS thread FPS and CPU; a sustained dip below sixty frames per second plus a long flame-graph block indicates a synchronous task starving the event loop. Correlating the low-FPS window with what rendered or executed at that moment isolates the cause.

COMMON WRONG ANSWERS: Relying only on console logs, which add overhead and reveal nothing about timing. Blaming the network layer when the symptom is a frozen JS thread. Confusing the JS thread with the native UI thread; a janky animation may actually be a blocked JS thread failing to feed updates.

LIKELY FOLLOW-UPS: Difference between JS thread and UI thread jank, how the legacy bridge contributes to dropped frames, why Flipper itself can skew measurements, and the move toward React Native DevTools as Flipper is deprecated.

ONE CONCRETE EXAMPLE: A list scroll stuttered on item tap. The profiler showed every tap re-rendered the entire list because the parent passed a new inline callback each render. The performance plugin confirmed a JS thread spike aligned with the stutter. Wrapping the callback in useCallback and memoizing rows removed the re-render storm and restored smooth scrolling.