How can I improve my shop speed and reduce cumulative layout shift?

Shopify Discussion

Topic summary

Issue: A store owner asks which apps can improve Cumulative Layout Shift (CLS), Total Blocking Time (TBT), and Speed Index on Shopify.

Latest guidance: An expert advises apps aren’t necessary; improvements can be achieved via theme/code optimizations and ongoing monitoring.

Key optimizations:

  • CLS (visual stability): Specify image/video width and height to reserve space; use gentle CSS transitions; preload fonts and critical CSS.
  • TBT (main-thread blocking): Minimize and remove unused JavaScript; use async/defer; implement lazy loading; reduce third‑party scripts.
  • Speed Index (perceived load speed): Prioritize critical resources; compress/modernize images (e.g., WebP); minimize/inline critical CSS; leverage browser caching.

Monitoring tools recommended: Google PageSpeed Insights, Lighthouse (Chrome DevTools), WebPageTest, GTmetrix.

Outcome/status: Clear optimization plan provided; no apps recommended. The thread remains open with an offer for further assistance and no confirmed resolution yet.

Summarized with AI on January 22. AI used: gpt-5.
1

please what apps can I use to adjust my cumulative layout shift, total blocking time, and speed index?

2

Hello @hunchostore ,

For managing CLS, TBT and Speed Index you don’t need to install any apps, With some basic changes in theme this things can be manage.

1. Cumulative Layout Shift (CLS): Cumulative Layout Shift measures the visual stability of a web page. It occurs when elements on a page shift their position as the page loads, which can be jarring for users. To fix CLS:

  • Specify Dimensions: Always include width and height attributes for images and videos in HTML to reserve space and prevent layout shifts.
  • Use CSS Transitions: When changing element sizes or positions, use CSS transitions to create smooth animations that minimize abrupt shifts.
  • Preload Fonts and CSS: Preload fonts and critical CSS to ensure that they are available as early as possible during page loading.

2. Total Blocking Time (TBT): Total Blocking Time measures the time during which the main thread of the browser is blocked and unresponsive due to JavaScript execution. To improve TBT:

  • Minimize JavaScript Execution: Reduce unnecessary JavaScript and optimize its execution. Remove unused scripts and use async/defer attributes where appropriate.
  • Lazy Loading: Implement lazy loading for images and other resources so that they are only loaded when they come into the viewport.
  • Reduce Third-Party Scripts: Limit the number of third-party scripts, as they can significantly impact TBT.

3. Speed Index: Speed Index measures how quickly the content of a page is visibly populated. It’s an indicator of perceived load speed. To improve Speed Index:

  • Prioritize Critical Resources: Ensure that critical resources like stylesheets and scripts needed to render above-the-fold content are loaded early.
  • Optimize Images: Compress and optimize images to reduce their size without sacrificing quality. Use modern image formats like WebP.
  • Minimize Render-Blocking CSS: Minimize and inline critical CSS to prevent delays in rendering.
  • Use Browser Caching: Leverage browser caching to store resources locally, reducing the need to fetch them repeatedly.

To assess and monitor these metrics, you can use tools like Google PageSpeed Insights, Lighthouse (available in Chrome DevTools), WebPageTest, or GTmetrix. These tools provide insights into the performance of your website and offer suggestions for improvement.

Keep in mind that improving these metrics requires a combination of technical optimizations, efficient coding practices, and ongoing monitoring to ensure a smooth and fast user experience on your website.

If you need further help do let me know.