Page Speed Checklist

A Core Web Vitals checklist is an ordered list of concrete fixes for LCP, INP and CLS, ranked by how much each one actually moves the score — not a vague "optimize your images" audit summary. Every item here is tagged by metric and impact, so you can fix what your real data says is actually failing.

🕒 Updated September 28, 2026 ⚡ 20 actionable fixes 💾 Progress saved in your browser 🆓 Free forever ⭐ Rate this tool 📖 Read the guide

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LCP · Largest Contentful Paint
Add <link rel="preload" as="image"> for the hero/LCP image so the browser fetches it immediately instead of discovering it late in the HTML.
Everything else is delayed until the HTML document itself arrives — a slow TTFB caps how fast LCP can possibly be, no matter what else you fix.
Inline critical CSS and defer non-critical stylesheets and scripts so the browser can paint sooner.
Smaller file sizes than JPEG/PNG at equivalent quality directly cut download time for the LCP element.
Cuts round-trip time by serving assets from a location physically closer to the visitor.
Helps the browser prioritize and reserve space for the resource earlier, instead of discovering its size only after it loads.
INP · Interaction to Next Paint
Tasks over 50ms block the main thread and delay the browser from responding to clicks or taps — split them up with setTimeout, scheduler.yield, or a Web Worker.
Ad tags, chat widgets and analytics scripts often run unrelated JS on the main thread at exactly the moment a user is trying to interact.
Search-as-you-type, resize and scroll handlers that run heavy logic on every single event compound quickly under real usage.
Reading and writing to the DOM in alternating order inside the same handler forces repeated synchronous reflows.
Defer analytics pings, prefetching and other non-critical work to idle time instead of the main interaction path.
CLS · Cumulative Layout Shift
Give ad slots, iframes and embeds a fixed size (or aspect-ratio) up front so content around them doesn't jump when they load.
Without this, the browser can't reserve space before the media finishes loading, so surrounding content shifts.
Font swaps that change text size or spacing mid-load are one of the most common, least-noticed causes of layout shift.
Dynamically adding a banner, cookie notice or promo above what's already rendered pushes everything below it down.
General
Field data (CrUX) can take up to 28 days to reflect a change — lab data confirms the fix actually worked immediately.
Core Web Vitals thresholds and real-world results often differ significantly between the two — a fix for one doesn't guarantee the other.
Loading everything eagerly wastes bandwidth on content the user may never scroll to.
Cuts transfer size for HTML/CSS/JS with no quality tradeoff — usually a one-line server config change.
Bundles that include code for pages the visitor isn't on inflate parse and compile time for no benefit.

Why an ordered checklist beats a generic audit score

A Lighthouse or PageSpeed Insights score tells you a number is low — it doesn't tell you what to actually do about it, or which fix matters most. This checklist exists to close that gap: every item is tied to a specific metric (LCP, INP or CLS) and tagged with a real impact level, so fixing the highest-impact item for your worst-performing metric is always the obvious next step.

Core Web Vitals data comes from real user field data (CrUX), which means fixes take time to show up in Search Console — often up to 28 days. Checking items off here as you ship them keeps track of what's already been done while you wait for the field data to catch up. Two of the highest-impact LCP items — server response time and caching — are also exactly what the HTTP Header Checker inspects on a live URL.

For example, the top LCP fix is a single tag in <head>:

<link rel="preload" as="image" href="/hero.jpg">

which tells the browser to start fetching the largest above-the-fold image immediately, instead of discovering it only after parsing the rest of the HTML.

How to use this tool

  1. 1
    Find your weakest metric

    Run the page through PageSpeed Insights or check the Core Web Vitals report in Search Console, and note which of LCP, INP or CLS fails or is closest to failing.

  2. 2
    Filter the checklist

    Use the LCP, INP, CLS or Other filter to show only the items that affect that metric.

  3. 3
    Start with high-impact items

    Every item is tagged HIGH, MEDIUM or LOW impact. Work through the HIGH items first.

  4. 4
    Tick items as you ship them

    The progress bar tracks what is done, and your ticks are saved in this browser so they are still there when you come back.

  5. 5
    Re-test and share

    Re-run your audit after each change, and click "Copy checklist" to share progress with your team.

Common use cases

  • Planning a fix sprint after Search Console marks URLs as "Poor" or "Needs improvement".
  • Handing developers a prioritized task list instead of a raw Lighthouse report.
  • Running a performance review before launching a new site or redesign.
  • Keeping track of which optimizations have already been made on a long-running project.
  • Showing new team members which fixes affect which metric.

Tips and common mistakes

  • Fix the template, not the page. Most Core Web Vitals problems come from a shared template, such as the hero image, font loading or an ad slot, so one fix can improve thousands of URLs.
  • Never lazy-load the LCP image. Lazy loading the main above-the-fold image delays exactly the element LCP measures.
  • Lab and field data differ. Lighthouse tests one simulated device, while Search Console uses 28 days of data from real Chrome users, so a perfect lab score can still fail in the field. INP in particular depends on real interactions.
  • Confirm server-side fixes. Caching and compression changes show up in response headers, which the HTTP Header Checker can confirm, and the HTML Formatter & Source Checker shows which scripts and stylesheets load in the head. The Core Web Vitals guide explains each metric in depth.

Frequently asked questions

LCP, INP and CLS are Google's field-measured page-experience metrics. Core Web Vitals is one of hundreds of ranking signals, so a page can still rank well without a perfect score — but consistently poor scores tend to correlate with worse engagement, which affects rankings indirectly.

INP (Interaction to Next Paint) officially replaced FID as the third Core Web Vital in March 2024. INP measures responsiveness across a page's entire lifespan rather than just the first interaction, making it a stricter and more representative metric.

Google Search Console's Core Web Vitals report, or PageSpeed Insights / the CrUX dashboard for field data on a specific URL. This checklist is for fixing issues once you know what's failing, not for measuring them.

No — start with the High-impact items under whichever metric your real data shows is failing. Fixing a metric that already passes wastes effort that could go toward the one that's actually holding your score back.

Yes, completely free with no signup. Your checked-off progress is saved only in your own browser's local storage — it's never sent to a server.

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Rahib Ali
Written & maintained by Rahib Ali
Senior PHP/Laravel Developer & Technical SEO Specialist, 12+ years experience · Updated September 28, 2026

Every item reflects INP — the metric that replaced FID in March 2024 — not outdated advice still floating around from before that change, and each fix is tagged with the impact level actually seen when applying it on real client sites.