TBT in the lab vs INP in the field

TBT in the lab vs INP in the field

These two measure the same kind of problem, your page being busy and unresponsive, but from different seats. TBT (Total Blocking Time) is a lab number from one test run. INP (Interaction to Next Paint) is the real-visitor version Google ranks on.

Think of TBT as a practice exam and INP as the real grade.

When to use which:
— You have no field data yet (new or quiet page): watch TBT, since it predicts INP well.
— You have real traffic: trust INP, because it counts actual taps.

Try this: if your lab TBT is high, expect INP trouble before it shows in the field, and start trimming heavy JavaScript now. TBT is your early warning light. Acting on it early is much easier than firefighting later.