Measuring Core Web Vitals Before and After Flying Scripts

Before configuring Flying Scripts, establish a baseline. Without before and after measurements, you cannot tell whether the plugin is actually helping or whether changes you make are having the expected effect.

Which Metrics Flying Scripts Affects

Flying Scripts specifically targets two Core Web Vitals metrics:

• Total Blocking Time (TBT) — The total time the main thread is blocked by JavaScript tasks longer than 50ms. Delaying non-critical scripts reduces TBT directly.
• Time to Interactive (TTI) — How long until the page is fully interactive. Fewer scripts running on load reduces TTI.

Flying Scripts does not improve Largest Contentful Paint (LCP) or Cumulative Layout Shift (CLS). If those are your weak metrics, this plugin will not help them.

Getting a Baseline with PageSpeed Insights

1. Go to pagespeed.web.dev and enter your URL.
2. Run the test on Mobile (the harder target — if mobile is good, desktop will be too).
3. Note the TBT score and value in milliseconds.
4. Screenshot or write down: Performance score, TBT, TTI, and the Reduce JavaScript Execution Time diagnostic.
5. Run the test three times and take the middle result — PageSpeed Insights has variance.

Using Chrome DevTools for Accurate TBT Measurement

PageSpeed Insights uses a simulated device. For more accurate local measurement:

1. Open Chrome DevTools (F12).
2. Go to the Performance tab.
3. Click the settings gear and enable CPU throttling (4x slowdown simulates a mid-range mobile device).
4. Click the record button then reload the page.
5. After the page loads, stop recording.
6. Look at the Total Blocking Time value in the summary at the top.

The red blocks in the Main Thread section are long tasks. Clicking on them shows which scripts are causing them. This tells you exactly which scripts contribute most to your TBT and which to prioritise for delay.

After Configuring Flying Scripts

Wait at least 10 minutes after saving Flying Scripts settings — Cloudflare or your caching plugin may serve a cached version without the changes. Clear all caches. Then rerun the PageSpeed Insights test three times and take the middle result.

A typical result from delaying Google Tag Manager and a live chat script: TBT reduction of 200-600ms and a 5-15 point improvement in the performance score. Results vary significantly based on which scripts you delay and how heavy they were.

Verifying Scripts Are Actually Being Delayed

Open Chrome DevTools Network tab. Reload the page. Filter by JS. The scripts that Flying Scripts is targeting should not appear in the initial load. After moving your mouse or scrolling, the scripts should appear as new network requests. If you see the target scripts loading immediately without any interaction, the keyword configuration is not matching the actual script URL. Check the exact URL of the script in the Network tab and compare it to your keyword.

WebPageTest for a Second Opinion

WebPageTest at webpagetest.org provides a waterfall chart that shows exactly when each script loads relative to the page load timeline. Use this to confirm that delayed scripts load after initial render and to identify any other heavy scripts not yet configured in Flying Scripts.

For a full site performance audit including Core Web Vitals analysis and a prioritised list of optimisation actions, a WordPress performance developer can review your specific setup and implement targeted improvements.