Comparison
Interaction to next paintvsTotal blocking time
Interaction to next paint
you clicked the checkbox and it took most of a second before the tick appeared.
The latency of the worst interaction on the page, measured from input to the next frame that reflects it, covering input delay, handler execution and rendering. It replaced first input delay because it measures the whole interaction and every interaction, not just the first and not just the waiting. It is dominated by main-thread work, so the fixes are the ones that make the main thread free: less JavaScript, smaller re-renders, work moved off the critical interaction.
Full entry →Total blocking time
the lab report says two seconds of blocking time and you can see it as a wall of yellow in the profile.
The sum of the part of every long task that exceeds fifty milliseconds, between first contentful paint and interactivity. It is the lab stand-in for responsiveness, because a synthetic run has no real interactions to measure. Improving it and improving interaction to next paint usually mean the same work, which is why it is the number to watch in CI.
Full entry →