Why Performance Matters

Web performance is not a nice-to-have feature. Research consistently shows that slower websites have higher bounce rates, lower engagement, and worse conversion rates. Google uses page speed as a ranking factor, and Core Web Vitals have become a measurable standard that affects your search visibility.

The good news is that most performance problems have well-understood solutions. A systematic approach to measuring, diagnosing, and fixing bottlenecks can produce dramatic improvements.

Core Web Vitals

Google's Core Web Vitals provide three metrics that capture the most important aspects of user experience:

  • Largest Contentful Paint (LCP) measures how quickly the main content appears, targeting under 2.5 seconds
  • Interaction to Next Paint (INP) measures responsiveness to user input, targeting under 200 milliseconds
  • Cumulative Layout Shift (CLS) measures visual stability, targeting a score under 0.1

These metrics give you concrete targets to optimize against. Use tools like Lighthouse, PageSpeed Insights, or the Chrome User Experience Report to measure your current performance.

Optimizing Images

Images are typically the largest assets on a web page and offer the highest potential for improvement. Several strategies can reduce their impact:

<img
  src="hero.webp"
  alt="Dashboard screenshot"
  width="1200"
  height="630"
  loading="lazy"
  decoding="async"
/>
  • Convert images to modern formats like WebP or AVIF, which offer significantly better compression
  • Always include width and height attributes to prevent layout shift
  • Use loading="lazy" for images below the fold to defer their download
  • Serve responsive images with srcset and sizes to deliver appropriately sized files for each device

Reducing JavaScript

Excessive JavaScript is one of the most common causes of poor performance. Every kilobyte of JavaScript must be downloaded, parsed, compiled, and executed, making it far more expensive than equivalent bytes of HTML or CSS.

Strategies for reducing JavaScript overhead include:

  • Audit your dependencies and remove unused libraries
  • Use dynamic import() to load code only when it is needed
  • Choose lighter alternatives where possible, such as using native browser APIs instead of heavy utility libraries
  • Consider frameworks like Astro or Qwik that ship minimal JavaScript by default

Caching and CDNs

A well-configured caching strategy prevents the browser from re-downloading resources that have not changed. Set appropriate Cache-Control headers for your static assets and use content hashing in filenames to enable long-term caching with safe cache-busting.

Serving your assets through a Content Delivery Network brings them physically closer to your users. CDNs maintain copies of your files at edge locations around the world, reducing latency for every request. Most hosting platforms like Vercel, Netlify, and Cloudflare Pages include CDN delivery by default.

Measuring Continuously

Performance optimization is not a one-time task. Set up Real User Monitoring to track Core Web Vitals from your actual users over time. Integrate performance budgets into your CI pipeline to catch regressions before they reach production. The most effective teams treat performance as a feature that requires ongoing attention.