Why your website's speed matters: Core Web Vitals explained simply

“My website is slow” is a vague diagnosis. Google measures speed with three precise indicators: the Core Web Vitals. Understanding what they measure tells you whether your site really has a problem — and which one.

The three indicators, without jargon

LCP — how long until the main content appears

Largest Contentful Paint measures the moment the largest visible element on the page (often your main image or your headline) finishes rendering. In plain terms: how long before the visitor sees something useful.

Target: under 2.5 seconds.

INP — responsiveness to clicks

Interaction to Next Paint measures the delay between a visitor clicking and the page visibly reacting. This is what makes a site feel sluggish even though it is already displayed.

Target: under 200 milliseconds.

Worth noting: INP officially replaced the older FID metric in March 2024. If you read an article that still talks about FID, it is out of date.

CLS — how stable the page is

Cumulative Layout Shift measures layout jumps during loading. You know the feeling: you are about to click, an image loads above, everything shifts down, and you click the wrong thing. That is exactly what CLS measures.

Target: under 0.1.

The detail almost everyone misses

Google does not judge your site on your connection, nor on a single test. It uses data from real visitors (the CrUX dataset) and takes the 75th percentile: to pass an indicator, 75% of visits must get a good score.

What that changes in practice: your site can feel fast on your fibre connection and your recent computer while failing for a quarter of your visitors — typically on mobile, over 4G, on a three-year-old phone. Their experience is what counts, not yours.

Why this is a business topic, not a technical one

Two reasons, and the second matters most:

1. Search visibility. Core Web Vitals are part of the page experience signals Google uses. They do not replace the relevance of your content — a fast, empty site will not rank — but with comparable content, they are a tiebreaker.

2. Visitors who leave. A visitor who waits leaves, and they leave before even seeing what you offer. Your whole proposition, your care, your photos: never seen. That is the worst scenario, because it is invisible in your analytics.

What actually slows a showcase website down

In the vast majority of cases, the culprits are always the same:

• Images that are too heavy — a photo from a modern camera can weigh several megabytes. Resized and converted to WebP, it drops to a few dozen kilobytes with no visible difference.
• Do-everything themes and plugins — each plugin adds its JavaScript and CSS, including for features you never use.
• Web fonts — every downloaded variant delays the text from appearing.
• Third-party scripts — chat widgets, ad pixels, maps, embedded videos: they often run before your content.
• Undeclared image dimensions — the number one cause of layout shifts (CLS).

Why we build static sites

A showcase website does not need to recompute its pages on every visit: your “Services” page is the same for everyone. A static site generates the pages once, at build time. The server then only has to deliver them.

In practice, that removes the database, the server-side execution on every visit, and a good share of the unnecessary JavaScript in one go. What remains is HTML, CSS, and the strict minimum.

It is not a magic wand — you can bloat a static site too — but it removes the most common causes of slowness from the start, instead of trying to compensate for them afterwards.

Measure your own site

Two free tools, no account needed for the first:

• PageSpeed Insights (pagespeed.web.dev): enter your address. Look at the “Discover what your real users are experiencing” section — that one reflects your actual visitors. The “diagnostics” part below is a lab test, useful to identify causes, but it is not what Google uses.
• Google Search Console, “Core Web Vitals” tab: how your pages evolve over time, if your site gets enough traffic.

Test on mobile first. That is where problems show up.

In short

• LCP < 2.5 s, INP < 200 ms, CLS < 0.1
• Measured on real visitors, at the 75th percentile — not on your machine
• Images and third-party scripts are the usual suspects
• Speed does not make up for poor content, but good content nobody sees is worth nothing

We design sites that are fast by construction

That is a technical choice we make from the start, not a last-minute optimisation.

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Is your current site slow? Let’s talk: the quote is free and with no obligation.