Website speed and SEO: what to measure and improve

Use Core Web Vitals, PageSpeed Insights and k6 to diagnose loading, interaction and load issues.

April

2021

Website speed and SEO: what to measure and improve

Website performance covers content loading and responses to visitor actions. Google uses Core Web Vitals in its ranking systems, but good scores alone do not guarantee high rankings.

Current metrics

LCP measures when the main large element appears; a good result is 2.5 seconds or less.
INP measures responsiveness to interactions; a good result is 200 milliseconds or less.
CLS measures visual stability; a good result is 0.1 or less.

Assess these thresholds at the 75th percentile of visits, separately for mobile and desktop. All three metrics must meet their targets for a passing assessment.

Use complementary checks

PageSpeed Insights provides field data where enough observations exist and a Lighthouse lab analysis. Field metrics reflect real use; lab tests help diagnose causes. Missing field data alone tells you nothing about site quality.

Use k6 on an agreed test environment to assess server behaviour under load. Load testing answers a separate question about handling a defined stream of requests.

Prioritise improvements

Review server response, image sizes and loading, blocking resources, third-party scripts and reserved space for media. Start with pages essential to orders. After each change, repeat measurements under comparable conditions and test forms, payments and navigation. Review field data as new visits accumulate.

Related resources and services

Sources

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Website speed and SEO: what to measure and improve

Current metrics

Use complementary checks

Prioritise improvements

Related resources and services

Sources

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