Website speed optimization

Core Web Vitals targets

Thresholds described by web.dev for a good experience, measured at the 75th percentile of page loads, separately for mobile and desktop.

Field data and lab tests

Lab tests load a page in a controlled environment and give quick, repeatable numbers that help diagnose problems. Field data comes from real visitors on their own devices and connections, and reflects what people actually experience. The two often differ: a page can score well in a lab test on a fast connection yet feel slow to visitors on older phones. Using both, field data to find which pages matter and lab tests to work out why, avoids optimising the wrong things.

Low-traffic sites may not have enough field data, in which case lab tests on a simulated mobile connection are the main guide.

Common causes of slow pages

• Oversized images

  Large photos uploaded straight from cameras, not resized or compressed.

• Heavy scripts

  Sliders, page builders and plugins loading code on every page.

• Third-party tags

  Chat widgets, trackers and embeds each add requests.

• Web fonts

  Many font files or weights delaying text.

• Slow hosting

  Server response time adding delay before anything loads.

• Layout shifts

  Images or banners without reserved space pushing content around.

How optimization is approached

1. 01

   Measure

   Field and lab data collected for key pages.

   Output: Baseline

2. 02

   Diagnose

   Causes identified for each slow metric.

   Output: Prioritised list

3. 03

   Fix

   Highest-impact changes made first and tested.

   Output: Improved pages

4. 04

   Verify

   Re-measured; field data watched over following weeks.

   Output: Confirmed gains

Typical high-impact fixes

Mobile matters most

Google's documentation states that it uses the mobile version of a site's content for indexing and ranking, and many visitors arrive on phones. Mobile devices often have slower processors and connections than desktops, so pages that feel fine on an office computer may struggle on a phone. Testing and optimising for mobile first usually improves desktop performance as well.

Hosting and server response

Before a browser can show anything, the server must respond. Slow or overloaded hosting, missing caching or a distant server location add delay to every page. Page caching, a content delivery network and a reasonably specified hosting plan help, but they work best after the page itself has been made lighter. Upgrading hosting to compensate for oversized images and scripts tends to cost more for less benefit.

Server response time is visible in most testing tools and is a useful first check.

Keeping a site fast

Speed tends to degrade as new content and tools are added. Simple habits keep it in check: resize images before uploading, think twice before adding another plugin or tracking script, and re-measure key pages every few months. A short checklist for whoever edits the site prevents many of the problems that optimization later has to undo.

Why speed matters to a business

Visitors who wait for a page may leave before it loads, especially on mobile. Faster pages make forms, product listings and checkout feel more responsive and reduce frustration. Speed is one factor among many in how a site performs, alongside clear content and easy contact options, but it is one that can usually be improved with focused technical work.