Core Web Vitals for SaaS: A Practical Guide

What Are Core Web Vitals?

Core Web Vitals are a set of metrics that Google uses to measure the real-world experience of using a web page. There are three of them:

Largest Contentful Paint (LCP)

LCP measures loading performance. Specifically, it measures how long it takes for the largest visible element on the page (usually a hero image or a large block of text) to load. Google considers anything under 2.5 seconds to be good. Above 4 seconds is poor.

Interaction to Next Paint (INP)

INP replaced First Input Delay (FID) in 2024. It measures how responsive your page is to user interactions like clicks, taps and keyboard input. A good score is under 200 milliseconds. This metric matters because a page that is slow to respond to clicks feels broken, even if it loaded quickly.

Cumulative Layout Shift (CLS)

CLS measures visual stability. It captures how much the layout of a page shifts unexpectedly as it loads. You know the experience: you go to click a button and just as you click it, an image loads above it and the button jumps down the page. That is a high CLS score and it is exactly what Google is trying to penalise.

Why SaaS Sites Tend to Struggle

SaaS websites have some common characteristics that make Core Web Vitals harder to pass.

Heavy JavaScript frameworks

Many SaaS sites are built on React, Vue or other JavaScript-heavy frameworks. These can be powerful but they often push a lot of processing onto the browser, which slows down both LCP and INP scores.

Third-party scripts

Analytics tools, chat widgets, A/B testing platforms, ad tracking pixels. SaaS marketing teams love them. Every one of these scripts adds load time and can increase your INP score. A site with ten third-party scripts running in the background is fighting an uphill battle.

Large unoptimised images

Hero images are a staple of SaaS website design. They are also one of the most common causes of a poor LCP score. An uncompressed PNG or JPEG in a hero section will tank your loading time.

Dynamic content causing layout shifts

If elements on your page load asynchronously (ads, chat widgets, cookie banners popping in after the page loads), they can cause layout shifts that increase your CLS score.

How to Check Your Current Scores

There are three main tools for checking Core Web Vitals:

• Google PageSpeed Insights (pagespeed.web.dev): Enter your URL and get a score with specific recommendations. Free and easy to use.
• Google Search Console: The Core Web Vitals report shows your real-world data aggregated across all users. This is the data Google actually uses for ranking.
• Chrome DevTools: For developers, the Performance tab gives granular detail on what is causing issues.

Start with PageSpeed Insights. It gives you a score out of 100 and a prioritised list of recommendations, so you know where to focus first.

How to Improve Each Metric

Improving LCP

• Convert hero images to modern formats like WebP or AVIF, which are significantly smaller than JPEG or PNG
• Add the loading="eager" and fetchpriority="high" attributes to your hero image so the browser prioritises it
• Use a content delivery network (CDN) to serve assets from a server closer to the user
• Reduce server response time by upgrading your hosting if needed

Improving INP

• Audit your third-party scripts and remove any that are not essential
• Defer non-critical JavaScript so it loads after the page is interactive
• Break up long JavaScript tasks into smaller chunks so the browser can respond to user input between them

Improving CLS

• Always set explicit width and height attributes on images and videos so the browser reserves space for them before they load
• Avoid inserting content above existing content after the page has loaded
• If you use a cookie banner, make sure it does not push other content down the page when it appears
• Use CSS to reserve space for ads and embeds

How Much Do Core Web Vitals Actually Matter for Rankings?

This is the question everyone wants answered. The honest answer is: they matter, but they are not the most important ranking factor.

Google has consistently said that great content and strong backlinks outweigh page experience signals. You will not rank a slow site with excellent content above a fast site with terrible content. But when two pages are otherwise equal, Core Web Vitals can be the deciding factor.

The more practical reason to care about them is user experience. A slow, unstable page loses visitors before they have read a single word. Improving Core Web Vitals reduces bounce rates, increases time on site and generally makes your site more likely to convert the visitors you do get.

A Practical Starting Point

If you are new to this, start here:

1. Run your site through Google PageSpeed Insights
2. Note which of the three metrics is failing or needs improvement
3. Use the "Opportunities" and "Diagnostics" sections for specific, actionable recommendations
4. Work through the highest-impact changes first
5. Re-test after each change to track progress

Most SaaS sites have two or three issues that account for the majority of their Core Web Vitals problems. Fixing those will have a disproportionate impact on your scores.