Total Blocking Time

Definition: Total Blocking Time is the additive of all blocking tasks. It is, in effect, a simplified version of time to interactive that does not sit on the timeline for page load.

Why it's good: TBT allows us to understand how much of our code blocking the page rendering process. This will also let us see where user interactivity issues happen even after the page has been completed.

What to consider: Like with TTI, there must be a five-second quiet window where a long task does not occur. As a result, only customers that have waited on a page for that window will have a reported TBT. Any quick-clicking customers will not have a TBT. Additionally, TBT will not be reported for customers with extremely long functions that get frustrated and leave because the functions never stop before the customer has left. TBT leaves these two blind spots.