How to Improve Core Web Vitals on HubSpot CMS Without Rebuilding

Working on a HubSpot CMS site and can’t hit green Core Web Vitals? You’re in good company. The platform is flexible for marketers, but it often ships with bulky templates, render‑blocking scripts, and unoptimized assets that undercut performance.

According to the 2024 HTTP Archive Web Almanac, only 51% of sites pass Core Web Vitals, and 92% load third‑party scripts, with a median of 27 per page. That’s the landscape your team is competing in.

If you're managing SEO or site performance, you need more than generic fixes. This guide gives technical teams a clear framework to optimize CWV in HubSpot CMS without rebuilding. We’ll cover how to handle fonts, scripts, images, caching, and how to monitor success using actual field data.

Understanding Core Web Vitals for Website Optimization

Core Web Vitals are a set of performance metrics developed by Google that reflect how users experience your website in the real world. They measure three critical areas: how fast a page loads, how quickly it responds to user input, and how stable it feels during load. These metrics are based on real user data from Chrome and directly influence search rankings.

Largest Contentful Paint (LCP): Loading Speed

LCP measures the time it takes for the largest element above the fold, usually a hero image or headline, to become visible. A good score is 2.5 seconds or less (Google).

On HubSpot CMS, LCP is often slowed down by large image files, bloated image modules, or unused CSS. Use modern image formats like WebP, apply compression, preload key assets, and enable lazy loading for below-the-fold content. Prioritize minimizing render-blocking resources to accelerate the page's initial load time.

Interaction to Next Paint (INP): Input Responsiveness

INP has replaced First Input Delay as Google’s responsiveness metric. It captures how quickly the browser reacts to a user action, like a click or tap. Scores under 200 milliseconds indicate good responsiveness (Google).

Pages built in HubSpot often struggle with INP due to third-party scripts, custom modules with excessive JavaScript, or poor DOM structure. Audit your pages using PageSpeed Insights or WebPageTest to isolate delays, then reduce unused scripts and defer non-critical JavaScript to maintain a responsive experience across mobile and desktop.

Cumulative Layout Shift (CLS): Visual Stability

CLS tracks how much content shifts on the screen as a page loads. Google's threshold is 0.1 or less for a stable experience (Google).

Common causes in HubSpot CMS include images or iframes without fixed dimensions, fonts that load late, and scripts that inject content mid-load. To stabilize your layout, define width and height for all visual elements, use font-display: swap, and delay non-essential script execution until after the page has fully rendered. 

How HubSpot CMS Affects Core Web Vitals

HubSpot CMS offers convenience for content teams, but its architecture often complicates performance work. Without technical oversight, the system can drag down Core Web Vitals scores and hurt SEO.

Server-Side Rendering Slows Interactivity

HubSpot relies on server-side rendering, which helps static content load quickly. But once dynamic elements like tracking scripts enter the mix, they often block browser responsiveness, hurting INP, especially on mobile. To reduce delays, avoid unnecessary embedded tools and audit how each module affects load time and interactivity.

Templates Load More Than You Think

Many HubSpot themes are designed for flexibility, not performance. Modules load scripts globally, even when not needed. Add enough CTAs, embeds, or third-party tools, and your entire site becomes slower across all pages.

The result: higher time to interaction, layout instability, and CWV failures that negatively impact SEO. Use SEO tools to analyze performance across templates and restrict scripts to only where they are essential.

The Theme Foundation Impacts Results

A clean-coded theme built for performance gives you a stronger CWV baseline. Clean Theme Web Design Services prioritize performance from the start and give you more control over how content loads and responds.

If your site’s performance is struggling across URLs, consider a refactor or migration to a theme that supports modern best practices. A lighter theme reduces layout shifts, improves font loading, and makes image optimization more effective across mobile and desktop.

Optimizing HubSpot CMS for CWV: Best Practices for Performance

Improving Core Web Vitals on HubSpot CMS means working within its limitations while gaining control over how scripts, assets, and content are rendered. Below are tactical strategies for performance optimization that directly impact CWV metrics like LCP, INP, and CLS.

Image Optimization Using HubSpot’s CDN

HubSpot’s image fields auto-generate multiple sizes and formats, but they don’t compress aggressively. Compress assets manually before upload, target ideal dimensions per module, and default to WebP whenever supported.

For LCP-critical images (like hero banners), use HubL filters to serve the correct size variant and preload using a <link rel="preload"> tag. Lazy load non-visible images using loading="lazy" and monitor how many assets load before scroll using the Performance panel in DevTools.

Pro tip: Audit image payloads. Your hero image should stay under 150 KB and render within 1 second on a mobile 4G connection.

JavaScript Control and Script Governance

Third-party JavaScript is the most common cause of INP failures on HubSpot sites. Many themes inject tracking scripts globally even when unused. Audit templates and partials for default includes that load analytics, chat widgets, or form libraries.

Use the Design Manager to isolate script-injection points and add conditional logic with HubL. Defer non-essential scripts with async or defer, and use HubSpot’s tag manager only for critical pages. Avoid embedding marketing pixels via global headers.

Best practice: Limit JS execution time to under 200ms during initial page load. Tools like Lighthouse or WebPageTest will flag violations.

Font Performance and Layout Stability

HubSpot themes often rely on Google Fonts or custom font stacks that load late, triggering layout shifts. Use font-display: swap and preload fonts that are visible above the fold.

Self-host fonts via the File Manager or a custom module to avoid third-party latency. Also, check that fallback fonts align closely in x-height and weight to reduce CLS.

Technical note: Use rel="preload" with as="font" and type="font/woff2" plus crossorigin for fonts in the critical path.

Caching and Asset Delivery Optimization

HubSpot auto-minifies CSS and JS but doesn’t give granular control over cache headers. Still, you can reduce load by consolidating assets. Avoid modules that inject inline styles or scripts unless scoped narrowly.

Structure templates to minimize DOM depth and repeated code blocks. Avoid nesting more than 3–4 container levels, and keep reusable modules lean. Check total CSS+JS weight, aim for under 200 KB combined on key pages.

Mobile-first tip: Run your test pages with Lighthouse mobile emulation. If Time to Interactive is >5s, dig into third-party and module-level bloat.

Speed Budgets and Publishing Governance

Define performance targets by template: homepage under 1.5s LCP, blog detail under 2s INP, and CLS under 0.1 across all templates. Use Looker Studio with CrUX data to build dashboards by URL pattern or template.

Enforce a staging review process where devs or SEOs inspect CWV metrics before major content launches. Set strict rules for which embeds, widgets, or scripts are allowed, no exceptions, without a performance audit.

Governance process: Create a checklist for content teams that includes media size limits, embed restrictions, and required fields for image alt text and dimensions.

Case Study: Improving Page Performance and UX for Olelo AI

To support a high-stakes product launch, Olelo AI partnered with SmithDigital to build a scalable HubSpot CMS site using the Clean Theme, which is designed for speed, usability, and future content control.

The Challenge

Olelo had no existing site and faced a tight launch timeline. They required a clean design that loaded quickly, worked well across mobile and desktop, and supported a content structure their team could maintain. Speed and clarity were essential for building trust with early visitors.

The Solution

SmithDigital delivered a custom-configured HubSpot CMS site optimized for performance. The Clean Theme allowed tight control over images, fonts, and JavaScript. Key templates were designed to reduce layout shift, prioritize content, and keep load times under critical thresholds for Core Web Vitals. The team also created a content model that supported fast LCP and simplified updates.

The Result

The site launched on time with a structure that meets Google’s Core Web Vitals benchmarks. Olelo’s team can now scale and manage content without performance loss. The design supports clear user paths, faster load times, and improved mobile experience, which are all essential for early-stage growth.

This project demonstrates how technical SEO, combined with smart CMS configuration, can significantly improve a website’s performance from day one.

From Audit to Action: Improving CWV on HubSpot CMS

Optimizing Core Web Vitals on HubSpot CMS requires more than just fast templates. It takes tight coordination between SEO, development, and content teams to avoid regressions and deliver stable, high-performing pages.

With a clean theme, smart asset handling, and clear publishing workflows, your site can meet Google’s performance benchmarks and offer a better user experience across devices.

Need help optimizing Core Web Vitals on your HubSpot CMS site? Book a Clean Theme consultation to identify quick wins and performance improvements.