Core Web Vitals are Google's three user-centric metrics for how fast, responsive and stable a page feels to real people.
Core Web Vitals are a set of user-centric performance metrics defined by Google that measure the real-world loading, interactivity and visual stability of a web page: Largest Contentful Paint (LCP), Interaction to Next Paint (INP) and Cumulative Layout Shift (CLS).
Each Core Web Vital captures a different part of how a page feels. Largest Contentful Paint (LCP) measures loading, how long until the largest content element (usually the main image or heading) is rendered. Interaction to Next Paint (INP) measures interactivity, how quickly the page responds to user input; it replaced First Input Delay in 2024 as the responsiveness metric. Cumulative Layout Shift (CLS) measures visual stability, how much the page unexpectedly shifts around as it loads. Together they approximate the three things a user notices: is it there, does it respond, and does it stay put.
Core Web Vitals matter for two reasons. First, they are deliberately user-centric, they reflect the experience people actually have, not an abstract server metric, so improving them improves real satisfaction. Second, they are part of Google's page experience signals, which means they influence search ranking, so poor vitals can cost visibility as well as users. They are assessed on field data, the experience of real users at the 75th percentile, which is why the same page can pass in a lab test and fail in the field on real devices and networks.
Measure Core Web Vitals two ways: in the field with Real User Monitoring, which captures actual users at the 75th percentile, and in the lab with tools like Lighthouse for diagnosis. To improve LCP, optimise the largest element, faster server response, right-sized images, prioritised critical resources. To improve INP, reduce main-thread work by breaking up long JavaScript tasks so the page can respond to input. To improve CLS, reserve space for images and embeds and avoid inserting content above what the user is already looking at. Field measurement tells you whether the fixes actually helped real users.
| Metric | What it measures | Good threshold |
|---|---|---|
| LCP | Loading: time to render the largest content element | under 2.5 seconds |
| INP | Interactivity: responsiveness to user input | under 200 ms |
| CLS | Visual stability: unexpected layout shift | under 0.1 |
Ops Singularity ingests Core Web Vitals as part of the frontend telemetry it collects over OpenTelemetry, so a regression in LCP or INP after a release is caught, correlated to the change and the backend behind it, and resolved through a governed Action Ticket rather than only charted.
Interaction to Next Paint (INP) replaced First Input Delay (FID) in 2024 as the responsiveness metric, because INP measures the latency of all interactions, not just the first.
Yes. Core Web Vitals are part of Google's page experience signals and can influence search ranking, so poor vitals affect visibility as well as user experience.
On field data from real users, assessed at the 75th percentile, which is why they can differ from a lab test that runs on a fast machine and network.
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