Core Web Vitals: Why They Matter and How to Get Them Right

Core Web Vitals are a set of user experience (UX) metrics defined by Google. They focus on three key areas:

• Largest Contentful Paint (LCP): How fast your site loads its main content.
• First Input Delay (FID): How quickly your site responds to user interactions.
• Cumulative Layout Shift (CLS): How stable your site’s layout is during loading (no unexpected shifts).

Google has made it clear: passing these metrics is a ranking factor. While no one knows how much it impacts rankings, it’s a positive influence that can help boost your visibility on search engine results pages (SERPs).

Here’s where it gets tricky. Google tests Core Web Vitals in a controlled lab environment, using fixed parameters that don’t reflect the variety of real-world user experiences. This is like optimising your car’s emissions for a lab test while ignoring what happens on the road - a problem Volkswagen infamously encountered.

The Solution: To truly optimise your site, you need both lab data and field data. Lab data gives you a starting point, but field data - collected from real users on actual devices - shows you how your site performs in the wild.

Real User Monitoring (RUM) tools collect Core Web Vitals data from actual site visitors, considering their devices, browsers, and network conditions.

For example:

• A user on an old Android phone with a 3G connection may experience a vastly different performance than someone using the latest iPhone on 5G.
• Marketing campaigns often use tracking parameters (like UTM tags) in URLs, which can bypass caching systems, leading to slower performance - a detail only RUM can reveal.

RUM tools, such as RumVision, provide actionable insights by aggregating field data, breaking it down by page type (e.g., homepage vs. product page), and highlighting problem areas.

Optimising Core Web Vitals isn’t just about pleasing Google - it’s about creating a better user experience, which directly impacts your bottom line.

1. Know Your Audience

Your customers’ devices, browsers, and network conditions vary widely based on demographics, geography, and purchasing power. RUM tools help you understand these variations, so you can tailor your optimisations accordingly.

2. Differentiate by Page Type

Not all pages perform the same. Your homepage might be lightning-fast, but your product detail pages or marketing campaign URLs could be dragging down your overall performance. RUM helps you pinpoint these discrepancies.

3. Boost Conversion Rates

Faster, more stable websites lead to happier users, higher engagement, and better conversion rates. A smoother experience keeps customers on your site longer, reducing bounce rates and improving sales.

We recently worked with a merchant who had a high-traffic site bogged down by slow load times on campaign URLs. Their marketing efforts brought in significant traffic, but parameters in their URLs (e.g., “?utm_source=google”) bypassed caching systems, causing delays.

Using RUM data, we identified the issue, implemented a caching fix, and immediately improved load times for campaign traffic. This optimisation not only enhanced user experience but also boosted their ad ROI.

Here are some practical tips for improving your Core Web Vitals:

• Enable Caching:
  • Use full-page caching (e.g., Varnish) to speed up load times.
  • Ensure dynamic parameters like campaign URLs don’t bypass caching systems.
• Lazy Load Images:
  • Only load images as they come into the user’s viewport, reducing initial load times.
• Minimise JavaScript:
  • Reduce unused JavaScript to speed up interaction times.
• Optimise Fonts:
  • Use modern font-loading techniques to prevent layout shifts.
• Focus on High-Traffic Pages:
  • Use RUM data to prioritise optimisations for your most-visited pages.

• Google’s Core Web Vitals impact your rankings, but the real value lies in improving user experience.

• Lab data isn’t enough. Use Real User Monitoring (RUM) to understand how your site performs for real users across devices and networks.

• Optimising for Core Web Vitals is easier than you think. Once you have the right data, making targeted improvements is straightforward and cost-effective.

• Know your audience. Tailor your optimisations to your users’ devices and browsing behaviours for maximum impact.

Core Web Vitals aren’t just a technical checklist - they’re a powerful tool for aligning your site’s performance with your customers’ expectations. By investing in the right monitoring tools and acting on data-driven insights, you’re not just improving your Google rankings; you’re creating a faster, more enjoyable shopping experience that keeps customers coming back.