How do I check if a website is slow?

22 June 2026 · By John Carlsson

Run the page through a speed tool such as Google's PageSpeed Insights and look at Largest Contentful Paint. Google rates under 2.5 seconds as good. In the browser, press F12 and use the Network tab to see which files take longest to load. Test on a simulated slow mobile connection and at different times of day.

To check if a website is slow, browser developer tools (F12) include a Network tab showing how long individual resources take to load. Free online performance testing tools simulate a page load and report metrics like Time to First Byte, Largest Contentful Paint, and overall load time. Testing under simulated slow mobile connections gives a realistic picture. Running multiple tests at different times is advisable, as server load varies.

The subjective vs objective measurement of slowness

When you check if a website is slow, remember that 'slow' is partly subjective — a page that takes 2 seconds to display its main content might feel fast in a desktop browser on broadband and painfully slow on a phone with a patchy signal.

Rather than relying on how a page feels when you load it on your own fast machine, objective performance tools measure specific metrics: Time to First Byte (how long your server takes to start responding), First Contentful Paint (when any content first appears), and Largest Contentful Paint (when the main piece of content is fully loaded). Google's 'Good' threshold is an LCP under 2.5 seconds — if you're consistently above that, users are experiencing a slow site.

What to look for in the Network tab

Browser developer tools' Network tab (opened with F12 in most browsers) shows every resource loaded on the page: HTML, CSS, JavaScript files, images, fonts, and third-party embeds. Each one has a corresponding load time bar. The things to look for: any resource with an unusually long load time (a particularly large image, an external third-party script taking hundreds of milliseconds), the total page weight at the bottom, and the time until 'load' fires (the point at which all resources have loaded). This view tells you both how slow the page is overall and specifically which resources are contributing most to that slowness.

Check if a website is slow under realistic conditions, not ideal ones

Testing a page from your own fast broadband connection and seeing it load in 0.8 seconds doesn't represent the experience of a visitor on a mid-range phone with an average mobile connection. Google's Lighthouse tool (built into Chrome developer tools, also accessible via PageSpeed Insights) simulates a slower mobile connection by default — which is more useful for understanding real-world performance. The Core Web Vitals field data in PageSpeed Insights, drawn from actual Chrome user visits, is the most reliable indicator of what real visitors are experiencing on your site.

Key Takeaways

'Slow' needs objective measurement — rely on LCP (under 2.5s = good) not your own perception.
The F12 Network tab shows exactly which resources are contributing most to load time.
Test under simulated mobile conditions, not your own fast broadband connection.

Frequently asked questions

How do you check if a website is slow using objective measures?

Whether a site feels slow is partly subjective, because a page that seems fast on desktop broadband can be painfully slow on a phone with a patchy signal. Rather than relying on how a page feels on your own fast machine, use objective metrics. Time to First Byte shows how long the server takes to start responding, First Contentful Paint shows when any content first appears, and Largest Contentful Paint shows when the main content has fully loaded. Google's Good threshold is an LCP under 2.5 seconds; if you are consistently above that, users are experiencing a slow site.

What should I look for in the browser Network tab?

The Network tab in browser developer tools, opened with F12 in most browsers, lists every resource the page loads, including HTML, CSS, JavaScript files, images, fonts and third-party embeds, each with its own load time bar. Look for any resource with an unusually long load time, such as a particularly large image or an external third-party script taking hundreds of milliseconds. Also check the total page weight and the time until the load event fires, when all resources have loaded. This view shows how slow the page is overall and which resources contribute most to that slowness.

Why should website speed be tested on a mobile connection?

Seeing a page load in under a second on your own fast broadband does not represent the experience of a visitor on a mid-range phone with an average mobile connection. Google's Lighthouse tool, built into Chrome developer tools and also available through PageSpeed Insights, simulates a slower mobile connection by default, which is more useful for understanding real-world performance. The Core Web Vitals field data in PageSpeed Insights, drawn from actual Chrome user visits, is the most reliable indicator of what real visitors are experiencing on your site.