The summary.
THE NETWORK AND PERFORMANCE PANELS ANSWER QUESTIONS GUESSING CANNOT
Most people use only the console and elements panel, and miss the two that actually find problems.
THE ELEMENTS PANEL SETTLES CASCADE QUESTIONS DEFINITIVELY
It shows which rule won and what overrode it — which is what most styling confusion is.
ALWAYS THROTTLE PROCESSOR AND NETWORK WHEN MEASURING
Development hardware and connections conceal every performance problem.
Check the total transferred and the largest single item on any slow page.
THE TIMING BREAKDOWN SEPARATES WAITING FROM TRANSFERRING
They require entirely different fixes.
LEARN CONDITIONAL BREAKPOINTS AND BREAKING ON ELEMENT CHANGES
The first solves pausing inside a loop running thousands of times; the second finds what modified something when you do not know where.
Generate source maps, or a production stack trace is useless.
READ ALL LAYOUT VALUES, THEN WRITE ALL OF THEM
Interleaving reads and writes forces repeated layout recalculation.
TREAT AUDIT SCORES AS A STARTING LIST, NOT A TARGET
Optimising for the number produces changes that improve the number and nothing else.
