Time from requesting a page until the server sends the
first byte back. The earliest signal that something is
coming — a slow TTFB delays everything downstream, including
LCP.
LCP
Largest Contentful PaintCORE WEB VITAL≤ 2.5 s
When the biggest piece of content — hero image,
headline, video — becomes visible. This is what users perceive
as “the page has loaded”, and it's the metric your
rendering strategy affects the most.
CLS
Cumulative Layout ShiftCORE WEB VITAL≤ 0.1
How much the page unexpectedly jumps after elements
have rendered — you go to click a button and it moves. Scored
as a fraction of the viewport, not milliseconds. Lower is
better.
HOW IT RESPONDS: INP, TBT
INP
Interaction to Next PaintCORE WEB VITAL≤ 200 ms
Measures the full lifecycle of a click or tap —
input delay + processing + paint — and reports your
worst interaction across the whole visit.
🖱️
← input delay + processing + presentation
→INP
✓
next paint
TBT
Total Blocking TimeDIAGNOSTIC< 800 ms
Total time the main thread is stuck on tasks longer than
50 ms. While blocked, the page can't respond to clicks,
scrolls, or other inputs.