How Third-Party Apps Slow Down Shopify Stores

How Third-Party Apps Slow Down Shopify Stores Reducing 1000ms of Total Blocking Time (TBT) This article is part of my Shopify Performance Engineering Series. In my previous articles: How I Improved a Shopify Store’s Performance from 30% to 65% Optimizing Largest Contentful Paint in Shopify I covered the overall optimization journey and LCP improvements. In this post, we’ll focus on another critical metric: 👉 Total Blocking Time (TBT) What is Total Blocking Time (TBT) Total Blocking Time measures how long the browser’s main thread is blocked by JavaScript. When the main thread is blocked: user interactions are delayed scrolling becomes janky clicks feel unresponsive Even if the page looks loaded, it doesn’t feel fast. Identifying the Problem: While analyzing performance using Lighthouse and DevTools, I noticed: high Total Blocking Time long JavaScript execution tasks delayed interactivity At first, I suspected Google Tag Manager (GTM). But after deeper investigation, I found the real bo