Common PageSpeed Insights Issues and How to Fix Them
Certain warnings show up in nearly every PageSpeed Insights report, regardless of industry or platform — render-blocking resources, unused JavaScript, slow server response time. Understanding what these actually mean makes the difference between staring at a confusing technical list and knowing exactly what to ask a developer to fix.
Here's a plain-language breakdown of the most common issues.
Key takeaways:
- Most recurring PageSpeed warnings fall into a handful of common categories
- Render-blocking resources and unoptimized images are among the most frequent, highest-impact issues
- Server response time often points to a hosting or backend performance problem, not just front-end code
- Many fixes can be handled through caching, compression, and CDN configuration
- Some issues require developer involvement, while others can be addressed through CMS settings or plugins
The Most Common Issues, Explained
| Issue | What It Means | Typical Fix |
|---|---|---|
| Eliminate render-blocking resources | CSS or JavaScript files are delaying the page from displaying content | Defer non-critical scripts, inline critical CSS |
| Properly size images | Images are larger than needed for their display size | Resize and compress images to match actual display dimensions |
| Reduce unused JavaScript | Scripts are loaded but a large portion of the code isn't actually used | Remove unused libraries, split code, load scripts only when needed |
| Serve images in next-gen formats | Images are in older formats like JPEG/PNG instead of WebP or AVIF | Convert images to modern formats |
| Reduce server response time | The server takes too long to begin sending the page | Upgrade hosting, enable caching, optimize backend queries |
| Avoid excessive DOM size | The page has too many HTML elements, slowing rendering | Simplify page structure, paginate or lazy-load large content lists |
| Minimize main-thread work | Too much JavaScript execution is blocking the browser's main thread | Reduce or defer JavaScript, remove unnecessary third-party scripts |
Render-Blocking Resources
When a browser encounters a CSS or JavaScript file, it often has to fully download and process it before continuing to render the page. If these files are large or unnecessary for the initial view, they delay everything the visitor actually sees. Deferring non-essential scripts and loading critical styles inline are common ways developers address this.
Unoptimized or Improperly Sized Images
This remains one of the most frequent flags in any PageSpeed report. Serving an image far larger than its actual display size, or in an older format like JPEG instead of WebP, adds unnecessary load time. This is often one of the easiest issues to fix with meaningful impact.
Slow Server Response Time
Unlike front-end issues, slow server response time points to something happening before the page even starts building — often related to hosting quality, an unoptimized database, or a lack of server-side caching. This is one of the reasons hosting choice (covered in our hosting guide) directly affects PageSpeed scores.
Excessive JavaScript and Main-Thread Work
Modern websites often load many third-party scripts — chat widgets, analytics tools, marketing pixels — each adding processing overhead. When too many run simultaneously, they can block the browser's main thread, making the page feel unresponsive even after it visually appears to have loaded.
Practical Fixes by Issue Type
1. For Render-Blocking and JavaScript Issues
Work with a developer to defer non-critical scripts, remove unused libraries, and load third-party tools (like chat widgets) only after the main content has rendered.
2. For Image-Related Issues
Compress images, convert to modern formats, and ensure images are served at appropriate sizes for their actual display dimensions — this is covered in more depth in our image optimization guide.
3. For Server Response Time
Consider upgrading hosting plans, enabling server-side caching, or using a CDN like Cloudflare to reduce the distance data has to travel to reach visitors.
4. For Excessive DOM Size
Simplify overly complex page layouts, paginate long lists of content instead of loading everything at once, and lazy-load sections further down the page.
Common Mistakes to Avoid
- Adding more third-party scripts without reviewing existing ones: Every new tool adds overhead — periodically audit which scripts are actually still needed.
- Assuming all issues need custom development: Some fixes, like image compression or caching, can be handled through CMS plugins or hosting-level settings.
- Fixing symptoms without addressing the cause: A slow server response time won't be solved by front-end image compression alone — the underlying hosting or backend issue still needs attention.
Frequently Asked Questions
Can these issues be fixed without a developer?
Some can — image compression and certain caching settings are often available through CMS plugins — but issues involving JavaScript execution or code structure typically need developer involvement.
Will fixing these issues guarantee a perfect PageSpeed score?
Not necessarily, and a perfect score isn't the real goal — meaningful improvement in Core Web Vitals and real user experience matters more than reaching 100 across the board.
How often should I re-check my PageSpeed Insights report?
Reviewing it after significant site changes (new plugins, redesigns, added scripts) and periodically every few months helps catch performance regressions before they become significant issues.
Next Steps for Your Business
Understanding these common issues turns a confusing technical report into a clear, actionable to-do list.
Our team can diagnose and fix the specific issues flagging on your site, addressing both front-end and hosting-related performance problems.