A fast website is essential: it improves your visitors’ experience and improves your site’s visibility in search engines. This guide shows how to use Jetpack Boost to improve your site’s speed score, explains what each setting does, and offers advice if you’re not seeing the improvements you expected.
Why your site speed score matters
A faster site isn’t just a technical goal—it makes your content easier to reach, your visitors more likely to stay, and your site feel smoother all around.
Jetpack Boost provides a performance score based on Google PageSpeed, so you can see how your site performs and where there’s room to grow. You’ll see:
- A numeric score and letter grade for Mobile and Desktop
- A clear visual meter showing your performance level
- A history of your scores over time (available with a paid plan)
Mobile scores are often lower than desktop scores—don’t worry, that’s expected. Boost helps you improve both.
How Jetpack Boost helps speed up your site
Jetpack Boost focuses on front-end performance—what your visitors interact with. Boost helps pages load faster by optimizing CSS, JavaScript, images, and caching.
You can turn each feature on or off from WP Admin → Jetpack → Boost.
Optimize CSS loading
When a browser loads your site, it first looks at the design instructions provided by a site’s CSS (Cascading Style Sheets). These instructions define presentational details: colors, font sizes, etc. If the browser has to interpret all of these instructions before showing the page, it can slow things down.
Jetpack Boost solves this by identifying the Critical CSS—the instructions needed to load the visible part of the page—and puts that first. This means your site starts displaying sooner, even before everything else loads.
This can improve scores like First Contentful Paint and Largest Contentful Paint, which measure how quickly your content becomes visible.
- With the free version, you will need to regenerate Critical CSS manually when you make major changes.
- With a paid plan, Boost automatically updates your Critical CSS in the background when needed.
Cache site pages
When someone visits your site, WordPress builds the page from scratch. That takes time.
Page caching saves a ready-to-go version of your pages so visitors don’t have to wait. Caching can help reduce server response time and speed up repeated visits. It’s like handing out a finished copy instead of writing it again every time.
- Enable Cache Site Pages in Boost to load your content faster.
- If this option isn’t visible, it may be handled already by your hosting provider.
Defer non-essential JavaScript
Some scripts on your site—like popups, sharing buttons, or animations—aren’t needed immediately when the page loads.
Boost can defer these scripts so they load after your main content, helping the page load faster. This can improve render times and help with PageSpeed warnings like “Reduce JavaScript execution time.”
- Turn on Defer Non-Essential JavaScript to prioritize your main content.
- If something doesn’t work as expected, you may need to exclude a specific script or turn this off temporarily.
Concatenate JavaScript and CSS
Every CSS or JavaScript file your site loads is an extra request to your server—and each request slows down overall page loading.
Concatenation combines multiple files into one, which means fewer requests and faster loading. This helps reduce Total Blocking Time by making your site easier for the browser to process.
- Turn on Concatenate JS and Concatenate CSS to streamline how your site loads assets.
- If any designs or features break, you may need to exclude specific files. Learn how.
Use the Image CDN
Images are often the biggest contributor to slow sites. Boost’s Image CDN automatically resizes, compresses, and serves your images from high-speed servers around the world. This improves the Cumulative Layout Shift and overall page load time, especially on mobile.
- Turn on Image CDN to optimize all images across your site automatically.
- With a paid plan, you can adjust image quality and enable Auto-Resize Lazy Images, which helps images load only when needed—and at the right size.
Identify large images
Even with a CDN, oversized images can still lower your site speed. Keeping image dimensions appropriate helps both speed and layout stability. Boost includes a tool to help you spot the worst offenders.
- Use the Image Performance Guide to detect images that are too large for their space.
- Replace or resize them using an image editor or online compression tool.
If your speed score is still low
Jetpack Boost takes care of many technical optimizations, but it can’t fix every issue on its own. If you’ve enabled all Boost features and your score still isn’t where you’d like, other factors may be affecting your site’s performance. Here are some common next steps:
- Remove unused plugins or scripts – Extra code can slow down your site.
- Use a lightweight theme – Some themes are better optimized than others.
- Test with Google PageSpeed Insights – See what specific issues are being flagged.
- Talk to your hosting provider – A slow server (high TTFB) may need an upgrade or tuning.
Boost works best when paired with a clean setup and fast hosting. Think of it as part of the solution, not the whole package.
What Jetpack Boost helps with
Jetpack Boost is designed to improve how your site loads for visitors. It focuses on front-end performance and makes quick, impactful changes that can raise your speed scores. Specifically, Boost helps with:
- Faster delivery of CSS, JavaScript, and images
- Improvements to key Web Vitals:
- FCP (First Contentful Paint): When something first appears on screen
- LCP (Largest Contentful Paint): When the main content finishes loading
- CLS (Cumulative Layout Shift): How stable the layout is as the page loads
What Jetpack Boost doesn’t cover
While Boost helps with many common performance issues, it doesn’t handle everything. It does not address:
- Server or hosting-related slowness (like TTFB or slow response times)
- Unused code, plugins, or third-party scripts
- Guaranteeing a perfect score in Google PageSpeed or Lighthouse
If your speed score is still lower than expected after enabling all Boost features, other factors—such as your theme, plugin setup, or hosting environment—may be involved.
Want to go further?
Our Advanced Site Speed Optimization guide includes practical steps for deeper testing, cleanup, and improvements beyond what Boost covers. It’s a great next step if you’re ready to fine-tune your site even more.
Jetpack Support is here to help with Boost-specific features, but general performance tuning is outside our scope.
Still need help?
If Boost isn’t working as expected or you’re unsure whether a feature is active, reach out to Jetpack Support, and we’ll be glad to help.
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