Loading Speed

Time required for a web page to fully display and become interactive for the user, meaning that all content (text, images, scripts, style sheets, etc.) is available and usable. This is an essential factor of technical performance, but also a strategic lever for optimizing user experience and conversion rate.

🎯 Why it's crucial:

• A slow page generates frustration, increases the bounce rate, and can drastically reduce conversions, especially on mobile, where network constraints are stronger.
• Google now considers speed as an SEO criterion, notably through Core Web Vitals.

📈 Impact on conversions:

• According to a Google x Deloitte study, 0.1 second of loading gain can lead to an increase of +8 to +10% in conversion rate.
  → Full study here (Think with Google)
• On mobile, a page taking more than 3 seconds to load can see its bounce probability increase by +32%, or even more at 5 seconds (+90%).

🛠️ Measurement tools:

• Google Lighthouse (and PageSpeed Insights),
• WebPageTest.org,
• Chrome DevTools ("Performance" tab),
• Core Web Vitals report via Search Console or GA4,
• Tools integrated into CDNs (Cloudflare, Fastly, Akamai...).

⚒️ Optimization levers:

• Image optimisation (modern formats: WebP, compression, lazy loading),
• CSS/JS file minification, removal of unnecessary code,
• Use of a CDN to bring content closer to users,
• Prioritisation of above-the-fold content,
• Reduction of server calls (API, third-party scripts),
• Avoiding slowdowns caused by poorly loaded marketing tags or A/B testing tools.

🔍 In CRO:

A fast loading time:

• Reduces friction and makes the user journey smoother,
• Improves A/B test performance (less “flickering” on client-side tests),
• Contributes to the perceived reliability and professionalism of the site,
• Mechanically increases conversion, engagement and satisfaction rates.