Definition
INP replaced First Input Delay as the responsiveness vital, measuring worst-case interaction latency across a visit. Heavy JavaScript, giant DOM trees and third-party scripts are the classic offenders.
Why it matters
Responsiveness is where mobile revenue dies quietly - a 400ms tap delay reads as broken, and broken does not convert.
Formula
98th percentile interaction latency per page
Benchmarks
Under 200ms good; over 500ms poor
All glossary terms