Website Speed Test: Tools, Metrics, and Fixes

A website speed test helps businesses understand how quickly their site loads on mobile devices and computers, while identifying factors that affect the user experience. Rather than relying on impressions alone, you can use tools such as PageSpeed Insights and GTmetrix to review data, find causes, and choose the right solution.

This article explains how to run a website speed test, interpret common metrics, and follow a practical troubleshooting process. Results can vary depending on the device, network, server location, and time of testing, so it is important to understand trends and prioritize the right issues.

Why should you test website speed regularly?

Page speed is an important part of the digital experience. When a page loads slowly, users may leave before viewing a product, submitting a form, or completing a transaction. For an online store, service page, or advertising landing page, delays can disrupt the conversion journey. However, speed should not be treated as the sole cause of conversion problems; content, value proposition, design, and the purchase process also have an impact.

Websites often change over time: businesses add images, install plugins, update tracking code, or launch new features. These changes can make pages heavier or trigger requests to external servers. Regular testing helps uncover problems after updates, before marketing campaigns, or when users report slow loading.

• Assess the experience: Find out whether key page content appears quickly and reliably.
• Identify bottlenecks: Pinpoint oversized images, render-blocking resources, slow server responses, or disruptive third-party code.
• Track changes: Compare results before and after optimization, a redesign, or a feature launch.
• Prioritize resources: Focus on the pages and issues with the greatest impact instead of making changes based on guesswork.

Test pages with specific business roles, not just the homepage. For example, an online store should check its category, product, cart, and checkout pages; a service business might prioritize service pages, pricing, and contact forms.

How to test website speed with PageSpeed Insights

PageSpeed Insights (PSI) is a Google tool that analyzes a URL and recommends improvements. It combines simulated lab data with real-world experience data from Chrome users when suitable data is available. These two data types serve different purposes, so they should not be treated as a single measurement.

1. Open PageSpeed Insights: Enter the specific URL you want to test, such as a product page, rather than just the domain name.
2. Run the analysis: Review the mobile and desktop results separately. Mobile users often have different network and hardware conditions than desktop users.
3. Read the metrics: Start with Core Web Vitals and the performance section, then review diagnostics, opportunities, and related resources.
4. Record the results: Note the URL, device, time, and key issues so you can compare them after making changes.

Understanding key PageSpeed Insights metrics

LCP (Largest Contentful Paint) measures how long it takes for the largest content element in the viewport to appear, usually the main image or heading block. If LCP is high, check image size and format, when key resources load, server responsiveness, and whether resources are being delayed.

INP (Interaction to Next Paint) reflects how responsive a page is after interactions such as clicking a button or opening a menu. A poor score may be caused by long-running JavaScript, tasks blocking the main thread, or the interface having to update too much after an interaction. Investigate real behavior rather than removing code mechanically.

CLS (Cumulative Layout Shift) measures unexpected layout shifts. Ads, images without declared dimensions, fonts that load late, or newly inserted content can cause buttons and text to jump. Reserving space for images and dynamic elements is often a useful fix.

The overall performance score is one signal to guide your decisions, not the only goal. Review real-world data, individual metrics, and diagnostic details as well. If PSI has no real-world data for a URL, that does not mean the website has no users or that the page is definitely fast; the tool simply has no suitable dataset to display.

Testing with GTmetrix and understanding its report

GTmetrix analyzes the page-loading process and presents metrics, charts, and a list of network requests. Depending on the available features and plan, you may be able to choose a test location, device, or browser. Since test conditions may differ from PSI, use GTmetrix to investigate the loading process in detail rather than comparing scores from the two tools as if they were measured in the same environment.

1. Enter the full URL of the page you want to analyze and choose an appropriate test configuration, if available.
2. Review the performance and loading-time summary, then open the Waterfall chart.
3. Look for resources that take a long time to load, are large, or start loading late; pay attention to requests from third-party services.
4. After optimization, test the same URL again with a similar configuration to evaluate the change.

Waterfall shows the order and load times of resources such as HTML, CSS, JavaScript, fonts, and images. A file with a long load time is not always the most important cause: consider whether it blocks key content, loads on every page, or appears only in a less important area. The report may also flag resources loaded multiple times, content that needs compression, or requests to external services.

For example, a company profile page might include a large banner image, several fonts, and a third-party chat tool. If Waterfall shows that the banner takes a long time to load before the main content appears, you could optimize the image and how it is loaded. If the chat tool’s files load only after the main content, they may be a lower priority. Draw conclusions based on both the report and the actual page experience.

How to fix speed issues in priority order

After running a website speed test, do not try to fix every warning at once. Choose issues that appear on important pages, affect key content, or recur across multiple pages. Record the baseline before making changes, then test one group of solutions at a time to see what makes a difference.

1. Optimize images and above-the-fold content

Compress images, choose dimensions that fit the display area, and use modern formats when supported by your system. Avoid loading unnecessarily high-resolution images into small display areas. You can lazy-load images below the initial viewport, but do not delay the main image users need to see right away. Setting width and height lets the browser reserve space and helps prevent layout shifts.

2. Review JavaScript, CSS, and extensions

Remove plugins, apps, or code snippets you no longer use, and check whether analytics, advertising, chat, and video embeds really need to load on every page. Combining, minifying, or deferring resources can help, but test after deployment because code changes can sometimes break menus, forms, or purchasing features.

3. Check the server, caching, and content delivery

If HTML responds slowly or pages are consistently slow, consult your site administrator about server configuration, caching, the database, and a CDN if appropriate for your website architecture. Front-end optimization cannot fully compensate for a poorly performing server. After each change, clear or refresh the cache properly so test results reflect the latest version.

• Test important pages on both mobile and desktop.
• Record LCP, INP, CLS, and the key issues in the report.
• Prioritize large images, render-blocking resources, and elements that slow interactions.
• Make changes one group at a time, test website functionality, and then retest under similar conditions.
• Monitor performance regularly, especially after updating the design, plugins, or a campaign.

The LilyTech team can help businesses assess their websites, identify priorities, and coordinate technical optimization aligned with business goals. The scope of work should reflect the platform, website structure, and actual test results rather than applying the same formula to every site.

Conclusion: Run a website speed test to focus your optimization

PageSpeed Insights helps you review experience metrics and improvement suggestions, while GTmetrix supports detailed analysis of the loading process through reports such as Waterfall. When using both tools, consider the device, URL, test conditions, and key metrics instead of focusing only on the overall score. A website speed test is most valuable when repeated systematically: measure the baseline, address priority causes, check functionality, and test again.

If your website loads slowly, its scores are difficult to improve, or you are unsure where to start, contact LilyTech for advice on an assessment and optimization plan suited to your business’s actual needs.