Website Speed Optimization: Core Web Vitals Checklist

Slow pages can frustrate visitors before they have a chance to understand your offer. Performance is more than a technical detail: it can affect usability, search visibility and how people perceive the business. Website speed optimization, supported by Google’s Core Web Vitals, is therefore an important part of business website projects. This guide explains the three metrics, practical optimization techniques and a checklist for planning the work. Better scores alone do not guarantee higher rankings or more revenue.

What are Core Web Vitals, and why do they matter?

Core Web Vitals are three performance indicators that describe aspects of real user experience: how quickly main content appears, how stable the layout remains and how promptly the page responds to interactions. Google uses them within its assessment of page experience, but they are not the only factors in search rankings.

The three metrics are:

• LCP (Largest Contentful Paint): The time until the largest eligible content element is rendered. A good result is 2.5 seconds or less. The element is often a hero image, video poster or large text block.
• CLS (Cumulative Layout Shift): A measure of unexpected layout movement during the page experience. A good result is 0.1 or less. Late-loading ads and images without reserved dimensions can contribute to shifts.
• INP (Interaction to Next Paint): A responsiveness metric that replaced FID in 2024. It measures the time from an interaction, such as a click, tap or key press, to the next visual update. A good result is 200 milliseconds or less.

Assess these thresholds at the 75th percentile of real-user visits, separating mobile and desktop experiences. Meeting all three targets supports a better experience, but does not by itself establish an improvement in rankings or conversions. A weak metric can reveal a specific source of friction that deserves investigation.

Image optimization: a common source of improvement

Images can account for a substantial share of page weight, so media delivery is often worth investigating early. The right format, dimensions and loading strategy can improve LCP when image delivery is the bottleneck. Measure before assuming that images are the main problem.

Consider these approaches:

• Use suitable modern formats: WebP or AVIF can reduce file size compared with some JPEG and PNG files. Compare actual size and visual quality rather than assuming a fixed percentage saving.
• Serve responsive images: Use srcset and sizes to provide an appropriate resolution for the display instead of making mobile users download unnecessarily large files.
• Apply lazy loading selectively: Load below-the-fold images as they approach the viewport. Do not lazy-load a hero image that is the LCP element, because that can delay its appearance.
• Define dimensions: Provide image width and height so the browser can reserve space before loading. This helps reduce layout shifts.

Server-side performance with caching and a CDN

Even optimized content can feel slow if the server takes too long to respond. Caching and content delivery networks can help. Caching avoids repeatedly generating or downloading unchanged content, reducing server work and response time where it is appropriate.

A caching strategy may have several layers. Browser caching keeps static files on the visitor’s device. Server-side caching can retain reusable generated content. A CDN distributes cacheable resources across multiple locations so visitors can receive them from a nearby delivery point. This can be particularly useful for ecommerce audiences in different regions. Private, account-specific and transaction content must not be shared through an inappropriate cache rule.

The table summarizes common techniques and their typical areas of impact:

Technique	Primary impact	Typical complexity
Browser caching	Repeat-visit loading	Low
CDN integration	Network latency and time to first byte (TTFB)	Moderate
Image compression	Page weight and image-related LCP	Low
Code minification and splitting	Transfer, execution and rendering work	Moderate to high
Server-side caching	TTFB and server load	Moderate

Code optimization: CSS, JavaScript and rendering

Excessive code can delay rendering and make interactions less responsive. Heavy JavaScript work can keep the browser’s main thread busy when someone clicks a button, increasing INP. Reducing unnecessary work is therefore an important part of performance optimization.

The following changes can help address code-related delays:

• Minify files: Remove unnecessary whitespace and comments from delivered CSS and JavaScript to reduce transfer size.
• Prioritize critical CSS: Where appropriate, inline the styles needed for the first view and defer noncritical styles without breaking the layout.
• Schedule JavaScript appropriately: Use defer or async according to script dependencies and behavior rather than adding them indiscriminately.
• Remove unused code: Unneeded third-party plugins and old libraries can create hidden overhead.

These changes are easier to sustain on a sound technical foundation. Our web design services can include performance requirements from the start, rather than leaving every improvement to a later patch. The appropriate approach depends on the existing site and agreed scope.

How speed relates to SEO and conversions

Performance can affect business outcomes in two ways. Page experience contributes to Google’s ranking systems alongside many other signals, while slow interactions can create friction during form completion, adding items to a cart or checkout. A faster page does not automatically outrank a slower competitor, and there is no universal conversion uplift per second saved. Measure the effect on your own customer journeys.

Treat performance as part of a broader search strategy rather than an isolated score-improvement exercise. Our SEO services can bring technical performance, content and keyword priorities into the same plan. Evaluate search and business results separately rather than assuming one metric explains both.

A practical website speed optimization checklist

Use this sequence to organize the work, adapting each step to the measured bottlenecks:

1. Establish a baseline for LCP, CLS and INP using PageSpeed Insights or suitable measurement tools.
2. Review image dimensions, compression and whether WebP or AVIF is suitable.
3. Lazy-load appropriate below-the-fold media, but not the important LCP image.
4. Reserve space for images and video elements to reduce layout shifts.
5. Minify CSS and JavaScript and remove unused code.
6. Use defer or async for suitable scripts while preserving dependencies and functionality.
7. Configure browser and server caching rules for content that is safe to cache.
8. Assess a CDN for static resources where it addresses a real delivery issue.
9. Optimize web fonts, consider font-display: swap and load only required weights, while checking layout stability.
10. After deployment, measure again and compare laboratory findings with real-user field data where available.

Repeat the review periodically as new plugins, content and scripts are added. Performance is an ongoing maintenance responsibility, not a task completed permanently at launch.

How can I measure Core Web Vitals?

PageSpeed Insights, Lighthouse and the Core Web Vitals report in Search Console are common tools. Lighthouse provides controlled laboratory diagnostics, while Search Console reports available real-user field data. A normal Lighthouse run does not directly reproduce a full real-user INP measurement. Use lab and field evidence together to understand the problem.

How long does website speed optimization take?

Basic image and caching improvements may take a few days where the system allows straightforward changes. Deeper code optimization, infrastructure work or a CDN rollout may take several weeks, depending on the site. Agree on a schedule after identifying the bottlenecks and the required work.

How does INP differ from the old FID metric?

FID measured the delay before processing the first interaction. INP considers responsiveness across a page visit and includes the time until the next visual update. It therefore captures a broader part of the interaction experience and replaced FID as a Core Web Vital in 2024.

Can I improve performance on an off-the-shelf platform?

Yes, although the changes available depend on the platform and your access. Image delivery, scripts and caching may offer improvements within its limits. Check which parts of the checklist you can control before defining the scope. Do not close the project based on one homepage score. Measure category, product and checkout pages separately, and compare laboratory findings with real-user experience where data is available. Functionality must remain intact after the changes.

Plan a performance improvement project

A slow site can make important journeys harder to complete. Improving Core Web Vitals may involve images, code, caching and delivery infrastructure, but priorities should follow the evidence. Complete the quote request form to discuss the current site and a concrete improvement plan with HazırSoft.

Use the evidence from these page types to prioritize the next improvement while preserving the working customer journey.