LCP (Largest Contentful Paint) Optimizations

What Affects LCP

LCP measures how quickly the largest visible element (such as a hero image, banner, heading, or video) is rendered within the user's viewport. It is primarily affected by how fast the critical content in the visible area is delivered and displayed to the user.

In simple terms: The faster the browser can render the main visible element, the better the LCP score.

1. HTML Document Request

The initial HTML document request is the first step in loading any webpage and directly affects LCP because no visible content can appear before it's received.

Best Practices

• •Keep the HTML document size below 100KB. Avoid embedding unnecessary markup or large datasets.
• •Use HTTP/2 or HTTP/3 for the document request. These protocols enable multiplexing and reuse of connections, improving response times compared to HTTP/1.1.
• •Minimize SSR payloads. When using Server-Side Rendering (SSR):
• •Load only what's required for the initial viewport.
• •Avoid loading heavy or unused data during SSR.
• •Defer non-critical data fetching to the client side using lazy loading or SWR.
• •Optimize backend response time. Slow API calls used in SSR can delay HTML generation and worsen LCP.
• •Cache frequently accessed data using Redis or a CDN.
• •Avoid over-fetching from APIs.
• •Use parallel requests where possible.
• •Prevent duplicate Redux dispatches. Dispatching the same Redux action multiple times during SSR can duplicate data in the rendered HTML, increasing document size and slowing response time.

2. Images in the Initial View

Images, particularly those in the hero or banner section, often represent the largest visible element on a page and are a key factor in LCP.

Best Practices

• •Optimize image size and format.
• •Hero or banner images should ideally be under 100KB.
• •Smaller images should be around 20–30KB if optimized.
• •Use WebP or AVIF formats instead of JPEG or PNG.
• •Serve images over HTTP/2 or HTTP/3 for faster, parallel downloads.
• •Enable proper caching. Set appropriate response headers such as: Cache-Control: public, max-age=31536000, immutable.
• •Prioritize critical images. In Next.js, use the priority attribute in the Image component to signal the browser to fetch the image early.
• •Lazy load non-critical images. Any image below the fold should use lazy loading (loading="lazy") to avoid unnecessary early downloads.
• •Prevent layout shifts. Always define width, height, or aspect ratio for images to maintain layout stability and improve visual performance.

3. Fonts and Render-Blocking Resources

Fonts and render-blocking CSS or JavaScript can delay the first render of visible content, impacting LCP.

Best Practices

• •Preload critical fonts using link preload tag
• •Use font-display: swap to avoid blank text while fonts load.
• •Inline critical CSS (above-the-fold styles) or use Next.js' built-in optimization.
• •Defer or load non-critical JavaScript asynchronously to prevent blocking the main thread.

4. Resource Loading Strategy

Efficient loading ensures faster rendering of critical resources.

Best Practices

• •Use rel="preload" for important assets like hero images, fonts, or key scripts.
• •Compress assets using Gzip or Brotli.
• •Avoid redirects that add unnecessary latency.
• •Use a fast CDN with global edge caching to minimize Time to First Byte (TTFB).

5. Additional Techniques

• •Optimize the critical rendering path by prioritizing only essential CSS and JavaScript during initial load.
• •Reduce JavaScript bundle size through tree-shaking, code-splitting, and dependency trimming.
• •Monitor and optimize TTFB since a slow TTFB often correlates with poor LCP.
• •Use preconnect to establish early connections to critical domains
• •Measure and monitor LCP using:
• •Chrome DevTools (Performance tab)
• •Lighthouse
• •PageSpeed Insights
• •The web-vitals JavaScript library for real-user metrics

6. Benefits of These Optimizations

• •Critical content becomes visible faster.
• •Users consume less bandwidth, improving accessibility on slower networks.
• •Pages load faster and feel more responsive.
• •Improved Core Web Vitals lead to better SEO rankings.
• •Enhanced overall user experience across all device types.