Total Blocking Time (TBT)
Total Blocking Time is a lab metric that measures the total amount of time between First Contentful Paint (FCP) and Time to Interactive (TTI) where the Main Thread was blocked by a Long Task. It is a key diagnostic metric in Lighthouse reports for quantifying the severity of non-interactive time during the initial page load and correlates closely with INP.
Related web performance terms
- Tag Manager
A tag manager (like Google Tag Manager) is a system that allows marketing and business teams to add and manage third-party marketing tags (snippets of code for analytics, advertising, etc.) on a we…
- Third-Party Script/Tool
A third-party script or tool is any piece of code, functionality, or service that is provided by an external vendor and integrated into a website.
- Throttling (CPU & Network)
Throttling is a technique used in Lab Data tools (like Lighthouse) to simulate how a website would perform on slower devices or less reliable network connections.
- Time To First Byte (TTFB)
A foundational web performance metric measuring the time from when a user makes a request to when their browser receives the very first byte of the HTML response.