Core Web Vitals are three measurements Google uses to describe how a page feels to a visitor: how fast the main content appears, how quickly the page reacts, and whether things jump around while it loads. They are part of how pages are assessed for search, and they matter regardless of search, because slow and unstable pages lose visitors.
The three measurements
Largest Contentful Paint (LCP) is the time until the largest visible element, usually a hero image or a headline, has rendered. A good value is 2.5 seconds or less.
Interaction to Next Paint (INP) measures how long the page takes to respond visibly when someone clicks, taps or types. A good value is 200 milliseconds or less.
Cumulative Layout Shift (CLS) measures how much content moves unexpectedly during loading. It is a score without a unit, and a good value is 0.1 or less.
Lab data and field data
There are two ways to measure. Lab tools such as Lighthouse load the page once in a simulated environment. That is useful for finding problems while developing. Field data comes from real visitors on real devices and connections, and it is what Google uses for assessment. It is reported at the 75th percentile, meaning three quarters of visits must be at or better than the threshold.
A page can score well in the lab on a fast office computer and poorly in the field on a mid-range phone. When the two disagree, trust the field data.
Improving LCP
- Speed up the server response. Everything else waits for the first byte. Cache pages that do not change per visitor.
- Optimise the main image. Serve it in a modern format, at the size it is displayed, not a 4000-pixel original scaled down by the browser.
- Do not lazy-load the main image. Lazy loading is for images further down the page. The main one should load with high priority.
- Remove render-blocking resources. Large stylesheets and scripts in the head delay the first paint. Defer scripts that are not needed immediately.
- Host fonts yourself. Fonts loaded from another domain add connection time before text can appear.
Improving INP
Poor responsiveness is almost always caused by JavaScript keeping the browser busy. Reduce the amount of script on the page, especially third-party tags for advertising, chat and tracking, which are frequent offenders. Break long tasks into smaller pieces so the browser can respond in between. Load code for features further down the page only when it is needed.
Improving CLS
- Give every image and video a width and height, so the browser reserves the space before the file arrives.
- Reserve space for embeds, advertisements and banners.
- Avoid inserting content above what the visitor is already reading, such as a cookie notice that pushes the page down.
- Choose fallback fonts with similar proportions so text does not reflow when the web font loads.
How to work on it
Start with field data in search console, which groups your pages into good, needs improvement and poor. Pick the page template with the most traffic among the poor ones, since fixing a template fixes every page built on it. Use a lab tool to find the cause, make one change at a time and measure again.
Field data is collected over a 28-day window, so an improvement shows up gradually. Do not expect the report to change the day after a release.
Keep it in proportion
These measurements are one input among many. A fast page with nothing useful on it does not outrank a slower page that answers the question. The practical goal is to reach the good range on all three, so that speed is not holding back content that deserves to rank, and then spend effort on the content.
Summary
LCP is about loading, INP about responsiveness, CLS about stability. Measure with field data, fix per template and re-measure. Performance work is part of our SEO and digital marketing service, since most of these fixes live in the code. If your pages are in the poor range, we can find out why.