What it means
It shows how long the page is busy with heavy work and cannot respond promptly to user input.
Term in plain language
TBT
A lab metric measuring how long the main thread is blocked by long tasks.
Why it matters
A high TBT helps identify JavaScript and other work that makes the interface feel frozen.
Example
A large script blocks the menu interaction for 600 ms after loading.
Related pageRelated terms
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Redirect
An HTTP response that sends browsers and search crawlers from one URL to another.
Schema.org
A shared vocabulary of types and properties for machine-readable descriptions of web-page entities.
Structured data
Machine-readable markup that explicitly describes page entities and their properties.