What is measured
The audit uses laboratory TBT; up to 200 ms is a good target for a control run.
Performance and mobile experience
Total Blocking Time (TBT)
This check totals the time when long main-thread tasks prevent the interface from responding.
Pass criterion
Long tasks do not occupy the main thread enough to create a material input delay.
What to fix
Split heavy JavaScript, defer non-essential code and reduce third-party script work after loading.
Automation limit
TBT is a laboratory metric correlated with responsiveness but does not replace field INP.
Reference