Core Web Vitals: does your site pass?

Core Web Vitals are three measures Google uses to score the real experience of your visitors: how fast your page shows its main content, how quickly it reacts when someone clicks, and how stable it stays while it loads. A page is rated good when its largest element appears in under 2.5 seconds, responds to a click in under 200 milliseconds, and barely shifts its layout, with a movement score under 0.1. These three scores feed your Google ranking, and above all they decide how many people stay instead of leaving. Here’s what they really measure, how to read your own score without being a developer, and what it actually costs to fix them.

What are Core Web Vitals, in plain terms?

Core Web Vitals are three scores Google gives each of your pages by watching what your real visitors go through in the Chrome browser. The idea is simple: instead of judging a site on abstract technical criteria, Google measures three things a human feels straight away, namely display speed, responsiveness to clicks, and how steady the page stays while it loads. This is what the search engine calls page experience, and these three signals are its measurable core.

One thing about these measures changed recently, and the story matters so you don’t get fooled. Until March 2024, the second score was called FID and looked only at the response to the visitor’s very first click. Google replaced it with INP, a stricter measure that tracks responsiveness across the whole visit. The practical takeaway is blunt: any article, tool or provider still talking to you about FID is working from stale information, and you can safely assume their method hasn’t been updated in a while.

Here’s a point that reassures many of the business owners I work with: these scores aren’t invented by a machine that tests your site once in a vacuum. Google calculates them from your customers’ real visits, the ones recorded in a large anonymous dataset called the Chrome User Experience Report. Your score therefore reflects what actual people experience when they reach your site, from their own phone and their own connection, which makes it an honest thermometer rather than a showroom figure.

What do LCP, INP and CLS actually measure?

Each of the three measures answers a question every visitor asks without realizing it. LCP asks how long it takes to see the main content of the page. INP asks whether the page reacts quickly when you click or tap the screen. CLS asks whether the layout stays put or whether things jump around just as you’re about to click. Here are the exact thresholds Google uses to give each one a good score.

LCP, short for largest contentful paint, is the moment the biggest visible block of your page finishes loading, usually a large banner image, a video or a headline. Until that element is there, your visitor is staring at a half-empty screen and wondering whether your site even works. Loading under 2.5 seconds gives the impression of a serious business, while past four seconds a good share of people leave before they’ve even seen what you sell.

INP, short for interaction to next paint, measures how fast your page responds when someone acts on it, for example opening a menu, clicking a button or filling in a field. A page can appear quickly yet freeze for a moment after a click, because it’s busy processing code in the background, and that’s exactly the frustration INP captures. CLS finally scores layout jumps: you’ve surely tried to click a link that shifted at the last second because an image or an ad had just loaded above it, and that small annoyance carries a real cost in trust and in sales.

To make this concrete, picture a visitor opening your page on their phone in a waiting room. First they wait for your big header photo to appear, and it’s LCP that decides whether they wait one second or five. Then they tap your menu to find your prices, and it’s INP that decides whether the menu opens right away or after an awkward pause. As they read, a banner loads late and pushes all the text down, and it’s CLS that scores that jump. The three measures tell, end to end, the little story lived by every person who arrives at your site, and that’s the story Google tries to sum up in a score.

Do Core Web Vitals affect Google rankings?

Yes, Core Web Vitals feed into Google’s ranking, but their weight is smaller than SEO marketing likes to imply. Google has been clear on this for years: page experience is one of the signals, without ever coming ahead of the relevance and quality of your content. A slow page that genuinely answers the question can therefore stay above a fast but hollow one, something I check regularly in my clients’ results.

Where these signals become decisive is between two pages of comparable value. When Google hesitates between several results that cover the topic equally well, page experience acts as the referee, and that’s often the exact moment a first-page spot is won or lost. In a competitive field where everyone publishes decent content, a fast and stable site takes a quiet but real edge over its poorly tuned neighbors. That’s one more reason to look after these foundations alongside your work to rank your site on Google.

It helps to keep the scale in mind so you don’t over-invest. Passing all three thresholds won’t lift a thin page from the second page to the first on its own, and no amount of speed rescues content nobody wants to read. What it does is remove a handicap: a page that fails these scores is quietly held back, while a page that passes them is simply free to rank on its actual merits. Think of it as clearing the entry bar rather than winning the race.

But I’d urge you not to look at Google alone here, because the real win is elsewhere. A page that loads fast and doesn’t jump keeps far more visitors than a sluggish one, and those visitors who stay are the ones who fill in a form or place an order. Improving your Core Web Vitals therefore serves two causes at once, your position in the results and your conversion rate, which makes it one of the rare technical jobs whose return shows up quickly in sales. The same logic applies to readability on phones, a subject I go into in my article on responsive design.

How do you test your site’s Core Web Vitals?

The simplest test is free and takes two minutes with PageSpeed Insights, Google’s official tool. You open the page, paste your site’s address, run the analysis, and get your three scores shown separately for the mobile and desktop versions. It’s the starting point I recommend to any business owner before they even call a developer, because it gives an honest picture of where you stand in seconds.

One detail changes everything in how you read this report, and many people get lost in it. At the top, you see your real visitors’ data, what Google calls field data, calculated over the last twenty-eight days of genuine visits. At the bottom, you see a lab test, a simulation the tool runs on the spot, useful for finding the cause of a problem but not necessarily a reflection of what your customers experience. The score that counts for your ranking is the field one, and a young or low-traffic site will actually show that part empty, simply because it doesn’t yet have enough visitors for Google to compute a reliable average.

One last point will spare you a nasty surprise: look at your mobile score first, not the desktop one. Google evaluates your site the way it appears on a phone, because most searches now happen on mobile, often on a worse connection than the fiber at your office. It’s common for a site to show a nice green on desktop and a worrying orange on mobile, and it’s the mobile version that weighs on your ranking. So always test on a real phone as well as the tool, and you’ll see straight away what your customers live through.

For sites with traffic, Google’s Search Console offers a dedicated Core Web Vitals report, which groups all your pages by status, good, needs improvement or poor, and by type of problem. It’s the tool I open first when I take over an existing site, because it shows at a glance which families of pages struggle and why. If you discover on that occasion that whole sections of your site have issues, a proper website audit will keep you from fixing things at random and save you a lot of time.

How do you improve your Core Web Vitals?

Improving your Core Web Vitals means tackling the precise cause behind each bad score, not chasing a magic trick. Each measure has its usual culprits, and once you know them the job gets much clearer, even for someone who doesn’t code. Here are the concrete levers, from the most accessible to the most technical.

For display time, the first culprit is almost always the weight of your images. A banner photo exported at full resolution can weigh several megabytes when a well-compressed version, at the right format and the right size, fits in a few hundred kilobytes with no visible difference on screen. It’s the most rewarding lever and often the only one a non-technical owner can pull themselves, by resizing images before uploading them to the site. Two recent formats, called WebP and AVIF, produce far lighter images than the old JPEG at the same quality, and most modern sites can serve them automatically. One more setting helps a lot: telling the browser to load the big image at the top of the page first, the one your visitor sees before anything else. After that come quality hosting that responds fast, page caching so nothing is recalculated on every visit, and trimming the code that runs on load. A site built lean from the start has a head start, as I explain in my article on sustainable web design.

Responsiveness to clicks almost always comes down to the code running in the browser, what’s called JavaScript, and that’s the developer’s turf. Too many scripts, especially those added by plugins or ad tracking tools, clog the browser and make it slow to respond. The fix is to reduce that code, push back whatever isn’t essential to later, and break long tasks into smaller ones so the page can breathe between two clicks. Visual stability, in turn, is fixed by reserving the space of each image, video or ad in advance, and by handling font loading cleanly, so nothing pushes the content around once it’s on screen. This split is worth remembering: you can act on images yourself, but responsiveness and stability usually call for an expert hand in the code.

If you want an order to work in, start with the score that’s failing hardest on mobile, since that’s the one hurting you most. In practice, the image work almost always comes first because it’s cheap and moves the loading score fast, then the script cleanup for responsiveness, and finally the layout reservations for stability, which are quick once a developer knows where the jumps come from. Fix one thing, test again on PageSpeed Insights, and only then move to the next, because chasing all three at once is how people waste a weekend and break something along the way.

What does a site that passes Core Web Vitals cost?

The cost depends entirely on your starting point and the size of your site, but I can give honest ballpark figures from my day-to-day. On a small brochure site whose only trouble is heavy images and mediocre hosting, a few hundred francs of work is often enough to bring all three scores into the green. That’s the most common case among freelancers and small businesses, and it’s also the best ratio between effort spent and result gained.

The budget climbs as soon as the site gets complicated. An online store loaded with plugins, ad banners and tracking tools piles up the scripts that drag down responsiveness, and setting all that straight means reworking the code, sometimes the hosting, and testing page by page. That kind of job runs into the thousands of francs, because it mixes developer work with a real upfront diagnosis. It’s for these cases that I always open Search Console and PageSpeed Insights before quoting anything, so I know whether the problem is superficial or structural.

There’s one situation where the cost question flips, and I’d rather tell my clients plainly. When a site is built on shaky foundations, with an overloaded theme and dozens of plugins stacked over the years, patching it to gain a few tenths of a second can cost more, year after year, than rebuilding it cleanly. In that case, a well-run website redesign settles the Core Web Vitals along the way, together with the design and the structure, for a budget that ends up more reasonable than the string of repairs. The right move is to have both paths estimated before you choose.

So, should you really worry about them?

The answer depends on what your site does for you, and I’d urge you to weigh it rather than panic over a score. If you run a small brochure site that already loads fast on your phone and brings you a few enquiries a month, don’t make yourself ill chasing two tenths of a second, your energy is better spent on content and on your local presence. Core Web Vitals are a fine-tuning job, not the bedrock of your visibility.

As soon as your business genuinely depends on Google traffic, though, or you sell online, these three scores deserve your full attention. Every second of waiting and every layout jump costs you visitors who won’t come back, and at scale that shows up in revenue well before it shows up in rankings. The right order of priorities stays the one I’ve been repeating for fifteen years: useful, honest content first, then fast and stable foundations that show it off, never the other way around.

If you’re not sure which category your site falls into, start with the free PageSpeed Insights test, look at the field score on mobile, and judge for yourself. And if the result worries you or you’d rather hand the diagnosis to someone who’s done this for a long time, starting a project takes five minutes, and I’ll tell you honestly whether your site needs a tune-up or real work.