Core Web Vitals Fix Guide
Start with field data when it is available, then use PageSpeed Insights and Chrome DevTools to locate the element, task, or layout shift behind a poor result. Separate pages cover Largest Contentful Paint, Cumulative Layout Shift, and Interaction to Next Paint. The guide gives practical image, layout, script, and server checks, plus a log for the change and follow-up review. Its target table uses Google’s good thresholds at the 75th percentile; a lab score alone does not establish field performance.
What you get
- Current LCP, INP, and CLS threshold table
- Diagnosis and fix steps for each metric
- Code patterns for image priority and reserved dimensions
- A before-and-after working log and source links
Who it's for: Developers and SEO professionals responsible for site performance improvements.
What this guide is
The Core Web Vitals Fix Guide is a diagnosis-first PDF field guide for the three metrics Google reports on page experience: Largest Contentful Paint (LCP), Interaction to Next Paint (INP) and Cumulative Layout Shift (CLS). It works on one principle: use real-user data to decide whether a page has a problem, use a lab trace to find the cause, make one targeted change and then check field data again after deployment.
What is inside
A targets table sets out the good field thresholds at the 75th percentile (LCP at or under 2.5 seconds, INP at or under 200 milliseconds, CLS at or under 0.1) with the usual cause and first diagnostic for each.
The LCP page tells you to find the actual LCP element and read its timing phases (TTFB, resource load delay, resource load duration and element render delay), then fix whichever dominates: server response, cache and CDN path, a late-starting hero image, an oversized file, render-blocking CSS or scripts, or font loading when the LCP is text. It includes a short image code pattern with width, height and fetchpriority.
The CLS page covers recording a load in Chrome DevTools, giving images and video dimensions or an aspect ratio, reserving space for ads, embeds and cookie banners, choosing font fallbacks with similar metrics, animating with transform, and rechecking after load because shifts can happen on interaction.
The INP page separates input delay, processing duration and presentation delay, and covers breaking up long tasks, keeping event handlers narrow, avoiding needless DOM changes and monitoring in the field after release.
The last page has a diagnose-prioritise-verify table and a working log for URL, device class, metric, field window, failing element, fix owner and next review date.
How to use it
Start with CrUX or PageSpeed Insights field data for the page or origin. If field data is unavailable, the guide says not to invent a passing or failing score. Reproduce the problem in a lab trace, change one thing, then compare field data after release, tracking mobile and desktop separately, since a good lab score does not prove field users have a good experience. Each section links to the matching web.dev article for the full detail.
Who it is for
Developers and technical SEOs fixing a failing report in Search Console, and marketers who need to brief a developer with evidence instead of a screenshot of a score.
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Frequently asked questions
- Which metric should I fix first?
- Fix the one that fails in field data for your key pages. The guide's table gives the first diagnostic for each so you start from evidence.
- Why do lab and field results disagree?
- Lab runs use one device and network, while field data reflects your real visitors. Use the lab trace to explain causes and field data to judge outcomes.
- Does the guide need paid tools?
- No. It points to PageSpeed Insights, Chrome DevTools and the Search Console report, and notes that paid monitoring is optional if you need per-route real-user detail.
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