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Problems We Solve

Why Is Our Website Fine on the Office PC but Painfully Slow on a Phone?

A website slow on mobile loses the visitors most likely to call you. SpiderHunts finds what phones are downloading and cuts the site down to what they need.

Updated 3 min readBy SpiderHunts Technologies

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Quick answer — TL;DR

Sites feel fast on an office connection and a powerful desktop, then crawl on a mid-range phone over mobile data. The usual culprits are oversized images and video, too much JavaScript and third-party scripts. We measure on real phones, remove what the page does not need and serve images sized for the screen.

It loads instantly for you, and nobody else

You open the site at your desk and it appears straight away. You have probably visited it hundreds of times, so your browser has most of it cached. A potential customer standing in a car park on a mid-range phone with a patchy signal gets a white screen, then a banner image arriving in strips, then a cookie popup, then the page jumping as a chat widget loads.

Many of them give up before they see your phone number. You never hear about it, because people who leave a slow page do not write in to complain.

Why phones suffer more than desktops

It is tempting to blame the hosting. Sometimes hosting is part of it, but on most business sites the bigger issue is what the page asks the phone to download and run.

CauseWhy it hurts phones in particular
Huge hero images or background videoThe phone downloads a desktop-sized file over mobile data before showing anything useful
Heavy JavaScript from themes and buildersPhones have slower processors, so running the script takes far longer than on a PC
Third-party scripts: chat, tracking, review widgetsEach one makes extra connections, often to several servers
Web fonts loaded in many weightsText stays invisible until the fonts arrive
Popups and bannersThey load late, move the page and cover the thing the visitor came for

Each of these got added for a reason. The problem is that nobody ever took anything away, and nobody tested on the kind of phone your customers actually use.

What a slow phone experience costs

Mobile visitors are often the ones with the most urgent need: someone looking for a plumber, a solicitor's number or opening hours. If they wait and give up, they tap the next result.

Paid clicks are the sharpest version of this. You pay for the click whether or not the page loads in time for the visitor to see it. Google also measures page experience on real mobile visits, and a consistently slow site gives it one more reason to prefer a competitor.

How we speed a site up for phones

  1. Measure properly. We test on throttled mobile connections and look at the real-user data Google collects for your site, not a single score from a desktop test.
  2. List everything the homepage and key service pages download, with its size and who asked for it.
  3. Resize and convert images so each screen gets a file that fits it, in modern formats, with lazy loading for anything below the first screen.
  4. Remove or defer scripts the page does not need to show its content. Chat widgets and trackers load after the page is usable, or on the pages where they earn their place.
  5. Replace background video on mobile with a still image, and trim fonts to the weights that are actually used.
  6. Fix layout shift, so the button a visitor is about to tap does not jump away as something loads above it.
  7. Put caching and a content delivery network in front of the site where the hosting setup supports it.

We work through these in order of weight, so the changes with the largest effect on what a phone downloads come first. On WordPress sites that often includes replacing a page builder section or a plugin, which we discuss with you before touching.

What changes for visitors and for you

The first screen appears quickly, the phone number and the enquiry button are visible and tappable without waiting, and the page stops jumping. You get a before and after measurement taken the same way, so you can see what changed rather than taking our word for it.

We also leave a short list of rules for whoever adds content next: image sizes, which embeds to avoid, and how to check a page on a phone before publishing.

Is this what is happening on your site?

  • The site feels fine in the office but people mention it being slow
  • Most of your visitors are on phones, and most of your enquiries are not
  • The homepage has a video, a slider or a very large banner
  • Several plugins or widgets were added for chat, reviews or tracking
  • Google Search Console reports pages with poor mobile experience
  • You run paid ads to pages nobody has tested on a phone

FAQ

Frequently asked questions

The questions readers ask us after this guide.

Still have a question?

Ask us directly — a senior engineer will get back to you.

Ask about your project

Do we need a new website to make it fast on mobile?

Not usually. Most of the weight comes from images, scripts and plugins that can be changed on the existing site. We say so if the theme or builder itself is the obstacle.

Is cheap hosting the problem?

It can be one part. We check server response time separately, so you know whether moving host would make a real difference before paying for it.

Will removing scripts break our tracking?

We agree which tracking you rely on first, and keep it, loading it in a way that does not hold the page up.

What affects the cost?

How the site was built, how many templates need work, and whether a page builder or theme has to be partly replaced.

Keep reading

More on Problems We Solve

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  2. A senior engineer reviews itAnd comes back with questions, a realistic range and an honest view on fit.
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