Do excessive third-party-scripts increase CLS and lower Core Web Vitals scores?
Asked on Sep 11, 2025
Answer
Excessive third-party scripts can indeed contribute to increased Cumulative Layout Shift (CLS) and negatively impact Core Web Vitals scores by causing unexpected layout changes and slowing down page load times.
Example Concept: Third-party scripts can introduce layout shifts by dynamically injecting content or styles after the initial page load, leading to unexpected movement of elements. This can increase CLS, a Core Web Vital that measures visual stability. To mitigate this, consider deferring non-critical scripts, using static placeholders, or limiting the number of third-party scripts.
Additional Comment:
- Evaluate the necessity of each third-party script and remove any that are not essential.
- Use "async" or "defer" attributes on script tags to prevent blocking the main thread during page load.
- Consider loading third-party scripts after the main content has been rendered to minimize layout shifts.
- Monitor CLS using tools like Google Lighthouse or WebPageTest to identify problematic scripts.
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