TL;DR
NitroPack’s Remove Render-Blocking Resources feature removes or defers JavaScript files, allowing your content to appear sooner and improving key performance metrics like FCP, LCP, and INP, all automatically.
Ever landed on a page and waited just a bit too long to see anything meaningful?
That delay often comes from render-blocking resources—files that the browser must process before it can start drawing the page.
And it seems needless to say it, but these delays can hurt both user experience and Core Web Vitals.
That’s why NitroPack’s Remove Render-Blocking Resources feature is designed to intelligently remove or defer them—so your WordPress site loads faster and feels faster.
What Does “Render-Blocking Resources” Mean?
Render-blocking resources are files that prevent the browser from showing your page until they’re fully downloaded and processed. They typically include:
- Large CSS stylesheets
- Synchronous JavaScript files
- Fonts loaded without font-display: swap
- Third-party scripts injected into the head
And here’s how they do it in practice:
- A user lands on your website.
- The browser starts parsing the HTML from top to bottom.
- When it encounters a
<link rel="stylesheet">or a<script>tag without defer or async, it pauses HTML parsing. - The browser then downloads, parses, and executes that CSS or JavaScript file before continuing.
- Only after those render-blocking files are processed does the browser start painting pixels on the screen—rendering what the user sees.
Behind all this is the main thread—a single-threaded process in the browser responsible for parsing HTML, executing JavaScript, calculating styles and layout, painting pixels to the screen, and handling user interactions (like clicks, taps, or scrolls).
When render-blocking resources are queued up, they occupy the main thread, leaving no room for critical tasks like displaying content or responding to input.
This causes:
- FCP (First Contentful Paint) to be delayed—users see a blank screen longer
- LCP (Largest Contentful Paint) to slow down—especially for hero images or headlines
- TBT (Total Blocking Time) to increase—scripts block other browser tasks
- INP (Interaction to Next Paint) to worsen—user inputs feel unresponsive because the browser is still busy loading files
In short, render-blocking resources clog the main thread and stall everything else—from loading visuals to accepting input.
With vs Without Removing Render-Blocking Resources
Without optimization, the browser pauses rendering to fetch and execute every CSS or JavaScript file it encounters—leading to blank screens and delayed interactivity.
When these blocking elements are removed or deferred, the browser can prioritize visible content first. This dramatically speeds up First Contentful Paint (FCP), Largest Contentful Paint (LCP), and Interaction to Next Paint (INP), creating a smoother, faster experience right from the start.
| Scenario | Without Optimization | With Optimization |
| FCP (First Contentful Paint) | Delayed—browser waits for all resources | Loads early—non-critical files are deferred |
| LCP (Largest Contentful Paint) | Hero sections load late | Optimized paint of above-the-fold content |
| INP (Interaction to Next Paint) | Main thread remains busy | Thread freed up for faster interaction |
| Load sequence | Browser halts on each blocking file | Browser paints first, loads rest in background |
| User perception | Blank screen, slow buttons | Visual + interactive feedback arrives faster |
Why Removing Render-Blocking Resources Matters
Modern WordPress sites often rely on plugins, third-party scripts, page builders, and massive stylesheets—all of which pile up during the loading sequence.
By optimizing your JavaScripts, you’re:
- Unblocking the rendering path so content appears faster
- Prioritizing critical visual elements, not heavy background tasks
- Keeping the main thread responsive, so users can interact without delay
- Improving Core Web Vitals, especially LCP, and INP
When render-blocking resources are present, PSI and Lighthouse often trigger warnings like:
- Eliminate render-blocking resources
- Remove unused JavaScript
- Avoid chaining critical requests
- Reduce JavaScript execution time
NitroPack helps resolve all of the above by restructuring how and when JavaScript files are loaded, ensuring smoother, faster, and more efficient rendering.
NitroPack’s Remove Render-Blocking Resources Explained
NitroPack provides two powerful methods for handling JavaScript render-blocking—both accessible under the Remove Render-Blocking Resources setting in your JavaScript configuration.
Resource Loader Script
This method changes how your JS and CSS are delivered to the browser’s main thread. It reorders resource loading to ensure critical files are loaded first, and less important files are delayed or deprioritized.
Think of it as reprogramming the traffic lights of your page load—so the most important content gets through first, while the rest waits its turn.
This way, NitroPack:
- Frees the main thread early for painting content
- Keeps page structure intact
- Prevents non-essential scripts from blocking rendering
Delay Non-Critical Resources
This setting focuses on deferring JavaScript that isn’t needed immediately.
Here’s how it works:
- NitroPack scans your page and identifies scripts that aren’t essential to rendering the hero section (above-the-fold content).
- Those non-critical scripts are delayed until after the user starts interacting, such as clicking or scrolling.
This dramatically reduces main-thread congestion during load, which improves INP and TBT scores—while ensuring that nothing critical is delayed.
NitroPack vs Manual Optimization
Manual optimization demands deep technical knowledge—especially when it comes to deferring JavaScript, loading CSS non-blockingly, or improving metrics like INP and TBT. Each step requires precise adjustments, ongoing testing, and constant updates as your site evolves.
NitroPack does all of this for you automatically. It understands script dependencies, distinguishes between critical and non-critical resources, and applies optimizations in real time—so you can focus on growing your site, not debugging it.
| Feature | Manual Setup | With NitroPack |
| Defer JS with correct order | Risky and time-consuming | Automated and dependency-aware |
| Load CSS without blocking | Requires rewriting <link> tags | Done automatically |
| Identify critical vs non-critical JS | Requires manual auditing | Handled automatically |
| Optimize INP and TBT | Manual tweaks to JS execution | Instant improvements |
Test NitroPack yourself
How to Enable Remove Render-Blocking Resources in NitroPack
- Log into your NitroPack dashboard
- Go to Cache Settings
- Navigate to JavaScript and enable:
- Remove Render-Blocking Resources
- Use Resource Loader Script
- Delay Non-Critical Resources
- Save your changes
NitroPack will now optimize how scripts and styles are delivered, removing unnecessary blockers and prioritizing what really matters for speed and interactivity.
FAQs
What is considered a render-blocking resource?
Typically, CSS files and synchronous JavaScript in the <head> prevent the page from rendering until fully loaded.
Does removing them affect how my site looks or works?
No. NitroPack carefully distinguishes between critical and non-critical files to ensure that layout and functionality are preserved.
Can I use this with other NitroPack features like Lazy Load or Critical CSS?
Yes. In fact, this feature works even better when paired with them.
Does delaying JavaScript improve INP?
Yes. By keeping the main thread available for input handling, NitroPack helps reduce INP and TBT scores.
