Core Web Vitals: How to Improve Site Performance

What Are Core Web Vitals?

Core Web Vitals are a set of specific metrics that Google uses to measure user experience on web pages. Introduced as a ranking factor in 2021 and continually refined since, these metrics assess three critical aspects of the user experience: loading speed, interactivity, and visual stability.

In 2026, Core Web Vitals remain a confirmed ranking signal, and sites that meet Google's recommended thresholds consistently outperform those that don't, all other factors being equal.

The Three Core Web Vitals

Largest Contentful Paint (LCP)

LCP measures how long it takes for the largest visible content element (typically a hero image, video, or large text block) to fully render on screen. It represents how quickly users perceive the page as loaded.

Interaction to Next Paint (INP)

INP replaced First Input Delay (FID) in March 2024 as Google's interactivity metric. While FID only measured the delay of the first interaction, INP measures the latency of all interactions throughout the page's lifecycle and reports the worst one (with some outlier adjustments).

Cumulative Layout Shift (CLS)

CLS measures visual stability by quantifying how much visible content unexpectedly shifts during page load. Nothing frustrates users more than clicking a button only to have the page jump and hitting the wrong element.

How to Measure Core Web Vitals

Google provides several tools to measure Core Web Vitals:

• Google Search Console: The Core Web Vitals report shows field data aggregated across your entire site
• PageSpeed Insights: Analyzes individual URLs with both field data (from real users) and lab data (from simulated tests)
• Chrome DevTools: Performance panel provides detailed lab measurements for debugging
• Chrome User Experience Report (CrUX): Real-world performance data from Chrome users
• Web Vitals JavaScript library: Measure Core Web Vitals in your own analytics

Field data (from real users) is what Google uses for ranking, so always prioritize it over lab measurements when they differ.

How to Improve LCP

Optimize Images

Images are the most common LCP element. Optimize them by:

• Using modern formats like WebP or AVIF (30-50% smaller than JPEG)
• Setting appropriate dimensions and using responsive srcset attributes
• Preloading the LCP image with <link rel="preload">
• Avoiding lazy loading on the LCP image (it should load immediately)

Reduce Server Response Time

• Use a fast, reliable hosting provider
• Implement server-side caching
• Use a CDN to serve content from locations near your users
• Optimize database queries and API calls

Eliminate Render-Blocking Resources

• Inline critical CSS and defer non-critical stylesheets
• Add async or defer attributes to non-essential JavaScript
• Minimize CSS and JavaScript file sizes through minification
• Remove unused CSS and JavaScript code

How to Improve INP

Optimize JavaScript Execution

Heavy JavaScript is the primary cause of poor INP scores:

• Break long tasks into smaller chunks using requestIdleCallback or scheduler.yield()
• Reduce the amount of JavaScript loaded on each page
• Use web workers for CPU-intensive operations
• Debounce rapid-fire event handlers like scroll and resize

Reduce Third-Party Script Impact

• Audit all third-party scripts and remove unnecessary ones
• Load analytics and tracking scripts asynchronously
• Use facades for heavy widgets (load chat widgets only when clicked)
• Set resource hints (preconnect) for essential third-party origins

How to Improve CLS

Set Explicit Dimensions

• Always include width and height attributes on images and videos
• Use CSS aspect-ratio for responsive media elements
• Reserve space for ads with minimum height containers

Prevent Dynamic Content Shifts

• Avoid inserting content above existing visible content
• Use CSS contain property to isolate layout changes
• Load web fonts with font-display: swap and preload critical fonts
• Animate with transform and opacity instead of properties that trigger layout

Performance Optimization Best Practices

Beyond Core Web Vitals, these general performance practices improve overall site speed:

1. Enable compression: Use Brotli or Gzip compression for text-based resources
2. Implement caching: Set appropriate cache headers for static resources
3. Optimize fonts: Subset fonts to include only needed characters and use the WOFF2 format
4. Reduce HTTP requests: Combine files where practical and eliminate unnecessary requests
5. Monitor continuously: Set up real-user monitoring (RUM) to track performance over time

The Business Impact of Performance

Improving Core Web Vitals delivers measurable business results. Studies consistently show that faster sites achieve higher conversion rates, lower bounce rates, and better engagement metrics. Amazon famously found that every 100ms of latency cost them 1% in sales.

At Ekolsoft, performance optimization is built into the development process from the start, ensuring that websites meet Core Web Vitals thresholds at launch rather than requiring retroactive fixes. Whether you optimize yourself or work with a development team, prioritize performance as a fundamental quality attribute, not an afterthought.