Core Web Vitals: LCP, CLS, INP, and why they matter
Core Web Vitals are a small set of metrics that try to capture how a page actually feels to use: how fast it loads, how stable it stays, and how quickly it responds. They turn a vague sense of a slow, janky page into numbers you can improve.
Last updated
What the three metrics measure
Largest Contentful Paint (LCP) measures loading — how long until the main content of the page appears. Cumulative Layout Shift (CLS) measures visual stability — how much things jump around as the page loads. Interaction to Next Paint (INP) measures responsiveness — how quickly the page reacts when someone taps or clicks.
Together they describe the moments where a page most often frustrates people: waiting for content, mis-tapping because a button moved, and hitting an interface that lags. Each has a target threshold that marks a good experience.
Why they became a ranking factor
Search engines want to send people to pages that work well, so page experience became part of ranking. The Vitals are not the strongest factor — relevance still dominates — but between two similarly relevant pages, the better experience can win.
The larger effect is behavioural. Slow, unstable pages lose visitors before they read or convert, and that abandonment is itself a signal. Improving the Vitals tends to improve the outcomes ranking ultimately cares about.
Field data versus lab data
Vitals can be measured two ways. Lab data comes from a controlled test on one device and connection; it is useful for debugging but idealised. Field data comes from real visitors on real devices, and it is what actually feeds ranking.
The gap between the two is often instructive: a page that scores well in the lab can still fail in the field on slower phones or networks. Trusting field data keeps optimisation honest about the audience you really have.
How Kirti approaches this
Kirti is being built to fold performance checks into the technical stage of its audit, flagging pages that miss the Vitals thresholds and proposing the fixes — heavy images, blocking scripts, unstable layouts — for a brand’s team to approve.
Because the agent is in active development and not yet generally available, this guide keeps to the metrics themselves, which matter whatever stack your site runs on.