1. Separate lab and field data
PageSpeed Insights and Search Console may show Chrome field data when there is enough traffic. Lighthouse runs a controlled lab test. Missing field data does not mean a page is poor; there may be too few samples. Use lab findings to debug and field data to understand real impact.
Do not stop at the homepage. Product, article, service and contact pages can have different largest elements and interactions. Test mobile and desktop separately; keep the URL, date and change alongside the result.
- Record field and lab findings for the same URL side by side.
2. LCP: do not delay the main content
The LCP element is often a large heading or hero image. Identify it first in DevTools or Lighthouse. For an image, deliver an appropriately sized file, compress it well and avoid lazy loading a critical above-the-fold image. Make the resource discoverable from HTML rather than adding it only after delayed JavaScript.
For a video background, review its poster image and file size. If playback is not essential in the first moment, adjust loading strategy. When server response is slow, image compression alone cannot fix LCP; caching and hosting need attention too.
- Identify the LCP element, then measure its download and render time separately.
3. INP: reduce click and typing delays
INP measures how promptly the page gives visual feedback to interactions. Menus, filters, forms and basket actions matter. Long JavaScript tasks, heavy third-party scripts and expensive work on every keystroke can block the main thread.
Find the slowest interaction in the Performance panel. Remove unnecessary work, split long tasks, defer suitable operations and give immediate feedback. Hiding a delay behind an animation does not solve the underlying problem.
- Try the menu, filters and form on a lower-powered phone.
4. CLS: keep the layout stable
Width and height attributes let the browser reserve room for images. Ads, cookie banners, expanding panels and late-loading fonts can shift the layout too. A button moving just as someone tries to press it is frustrating and error prone.
Use layout shift traces in developer tools to find moving elements. Reserve space and place late content in its allocated area instead of pushing text down. Observe the page while it loads; a final screenshot alone can hide the shift.
- Watch the initial screen for movement as images, fonts and consent UI load.
5. Build a measured improvement plan
Choose the page type with the greatest real-user impact. Improve its main visual resource, then critical scripts, then layout shifts rather than changing everything at once. Compare equivalent lab conditions; field data updates over time.
Speed alone is not project success. Weak content, broken forms or unclear enquiry flows remain unhelpful even when they load quickly. Evaluate performance alongside accessibility and business goals.
- Record LCP, INP and CLS before and after the first fix.