Total Blocking Time (TBT)

Categories: T, SEO Glossary

Total Blocking Time (TBT) is a performance metric that quantifies the total duration of non-interactive periods between First Contentful Paint (FCP) and Time to Interactive (TTI). These non-interactive periods are instances when the main thread of a browser is blocked for a significant length of time, inhibiting user input response. TBT is particularly crucial for understanding the user experience during page load, as it helps identify the extent to which a user might experience delays when trying to interact with the page. In lab testing environments, TBT is often recommended as a proxy for the First Input Delay (FID), one of the Core Web Vitals, as it effectively captures the user experience before the page becomes fully interactive.