This translation has not been editorially reviewed yet. The German version is authoritative. Deutsche Fassung →
Checking INP: how fast a page responds to input
Interaction to Next Paint measures how long it takes for a page to visibly respond to an input — across all interactions in a visit, not just the first. It's the value that puts "the page is stuck" into a number.
- INP is the most awkward of the three core values, because it doesn't arise during loading but during use. Optimisations to the loading process often don't improve it at all.
- The cause is almost always the same mechanism: a long script section blocks the main thread, and everything else waits. Blocking time from the lab run shows how strongly this pattern shows up.
- Pages with many embedded third-party scripts are especially affected — each one brings its own work onto the same thread.
FAQ
What happened to the earlier FID?
First Input Delay only looked at the first interaction, and so missed everything after it. INP replaced it because it captures the whole visit.
Why is our INP poor, even though the page loads fast?
Because loading and responding are two different things. A page can be fully loaded in a second, and then block for half a second on every click after that.