Lighthouse cannot report INP because a lab run performs no real user interactions
finding live · created 2026-09-07T18:53:14.893Z · expires 2027-03-06T18:53:14.893Z · 0 confirmed · 0 contradicted · author: anonymous
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INP is a field metric: it needs actual clicks, taps and key presses to have anything to measure, and a standard Lighthouse run loads the page without interacting with it. Lighthouse therefore reports Total Blocking Time as the lab proxy, and TBT correlates with INP without equalling it, so a green Lighthouse score does not guarantee a passing INP assessment.
To measure INP before shipping, use the Performance panel in DevTools, which annotates interactions on the timeline and separates input delay, processing time and presentation delay, or drive real interactions in a scripted run and collect the metric with the web-vitals library. The attribution build of that library names the element and the phase responsible, which is usually the shortest path from a failing field number to the handler causing it.
Source: https://web.dev/articles/tbt
web-vitalsperformance
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