Quick Definition #
Website performance describes how quickly and reliably a page loads and responds. Core Web Vitals are Google’s user-experience metrics for loading performance, responsiveness and visual stability.
The Core Web Vitals #
| Metric | What it measures | Good target |
|---|---|---|
| Largest Contentful Paint (LCP) | Loading performance of the largest visible content element | 2.5 seconds or less |
| Interaction to Next Paint (INP) | Responsiveness across user interactions | 200 milliseconds or less |
| Cumulative Layout Shift (CLS) | Unexpected visual movement during loading | 0.1 or less |
These targets are assessed at the 75th percentile of page visits, segmented by mobile and desktop where data is available. Field data reflects real users; laboratory tests help diagnose problems under controlled conditions.
Common Performance Problems #
- Oversized hero images and other media.
- Too much JavaScript or long-running main-thread tasks.
- Slow server responses or inefficient caching.
- Fonts and embeds that delay rendering.
- Images, ads or widgets that shift layout after loading.
Improvement Workflow #
- Measure important page templates with field data and a lab tool.
- Identify the largest content element and check why it loads slowly.
- Compress images, serve appropriate dimensions and use modern formats where suitable.
- Reduce unnecessary JavaScript and defer non-critical work.
- Improve caching and server response where evidence points to backend delay.
- Reserve space for images, embeds and ads to reduce unexpected layout shifts.
- Retest after each meaningful change and monitor field data over time.
Example #
If a Knowledge Hub article’s large banner is the LCP element, serving a correctly sized compressed image and avoiding lazy-loading that above-the-fold image may help. If the page shifts when a font or embedded widget appears, reserve the needed layout space and review loading behaviour.
Performance and SEO #
Performance contributes to user experience and is one part of a broader page experience. Strong Core Web Vitals scores do not guarantee high rankings, and a technically fast page still needs relevant, useful content.
Common Mistakes #
- Optimising only a lab score and ignoring real-user data.
- Compressing images so aggressively that quality becomes poor.
- Removing useful functionality without measuring the impact.
- Assuming a plugin or caching toggle fixes every bottleneck.
- Expecting performance improvements alone to guarantee ranking gains.
Key Takeaway #
Measure the actual bottleneck, make targeted improvements and validate them with both controlled tests and real-user data.
FAQs #
What replaced First Input Delay (FID)? #
Interaction to Next Paint (INP) replaced FID as a Core Web Vital in March 2024.
Do Core Web Vitals guarantee a ranking increase? #
No. They are useful experience metrics, but search performance depends on many factors.
Related Topics #
See Technical SEO Fundamentals and Mobile SEO.
