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What are Core Web Vitals?

Short answer

Core Web Vitals are three metrics Google uses to measure real-world page experience: Largest Contentful Paint (LCP, loading speed), Interaction to Next Paint (INP, responsiveness to input, which replaced First Input Delay in March 2024), and Cumulative Layout Shift (CLS, visual stability). They are measured from real Chrome users via the Chrome User Experience Report.

By InstantPWA growth research·Reviewed July 25, 2026

The three metrics

LCP measures when the largest visible element renders; INP measures the latency of the slowest interaction during a visit; CLS measures unexpected layout movement.

Why PWAs can help

Cached repeat visits from an installed PWA tend to have near-instant LCP because assets load from the service-worker cache instead of the network.

How they are measured

Field data comes from real Chrome users (CrUX); lab data comes from tools like Lighthouse and PageSpeed Insights simulating a single load.

Sources

Related
Does a PWA help or hurt SEO?
A PWA does not directly change your Google ranking. Googlebot indexes your HTML the same whether or not you have a service worker. The indirect effect is Core Web Vitals: repeat visits from installed users have near-zero TTFB and better INP, which improves your CWV score and, over time, ranking.
How do you test a PWA with Lighthouse?
Open Chrome DevTools, go to the Lighthouse panel, select the categories you want (Performance, PWA-related checks live under "Best Practices" in modern Lighthouse) and click "Analyze page load". Lighthouse reports whether your manifest is valid, whether a service worker is registered, and whether the page is served over HTTPS.
What are PWA app shortcuts?
App shortcuts are quick-action shortcuts that appear when a user long-presses (mobile) or right-clicks (desktop) an installed PWA’s icon — similar to native app long-press menus. They are declared in the manifest’s "shortcuts" array, each with a name, url and optional icon, letting users jump straight to a specific feature like "New message" or "Search".
What are the criteria for "Add to Home Screen" to appear?
Chromium browsers offer "Add to Home Screen" once a site is served over HTTPS, links a manifest with at least a name, a 192px and 512px icon, a start_url and a standalone/fullscreen/minimal-ui display mode, and has registered a service worker with a fetch event handler. Some engagement (visiting the site more than once, with time between visits) is also typically required before the automatic prompt fires.
How does a PWA splash screen work?
On Android, Chromium automatically generates a splash screen for an installed PWA using the manifest’s name, background_color, theme_color and the largest available icon — you do not draw it manually. It appears briefly while the app’s first paint loads after the user taps the icon. iOS Safari does not generate one automatically and requires custom <link rel="apple-touch-startup-image"> tags per device size.