Why can INP not be measured in a lab?

Because it measures real interactions. A synthetic test loads the page with nobody clicking anything, so there is no interaction to time. Tools that display a lab INP are showing you a proxy, usually Total Blocking Time, relabelled — which is a different measurement of a different thing.

200ms or under is good, up to 500ms needs improvement, and above 500ms is poor — assessed at the 75th percentile of real visits.

What replaced FID and why?

INP replaced FID in March 2024. FID measured only the delay before an event handler began running, so a page that responded instantly and then blocked for a second scored well while feeling terrible. INP measures through to the next paint, which is when the user actually sees a response.

My site has no INP data. What do I do?

That means too little traffic for the Chrome UX Report, which is common and not a fault. Use Total Blocking Time as your lab proxy, and measure real interactions with the web-vitals JavaScript library on your own analytics if you need field numbers sooner.

How do I improve INP?

Find the slow interaction rather than optimising generally. Usually it is one handler doing too much synchronously. Paint the acknowledgement first, yield to the main thread, defer non-urgent work, and cut down the JavaScript that runs during interaction.

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Interaction to Next Paint (INP) Test

Check INP against the 200ms threshold — and understand why a lab test alone can never give you one.

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The short version

What is Interaction to Next Paint (INP) Test?

Interaction to Next Paint replaced First Input Delay as a Core Web Vital in March 2024.

It measures the full latency of an interaction — from the tap or click, through the work your JavaScript does, to the next frame the browser actually paints. FID only measured the delay before processing started, which flattered pages that acknowledged a click quickly and then froze. INP is harder to satisfy and much closer to what people mean by "this page feels slow". It is also a field metric: it requires real people interacting, so it can only come from the Chrome UX Report. If your site does not have enough traffic to appear there, INP is genuinely unavailable, and this tool says so rather than showing you a lab number dressed up as one.

Step by step

How to use Interaction to Next Paint (INP) Test

1
Enter your page
INP arrives with the PageSpeed response when the Chrome UX Report has enough data for the URL or its origin.
2
If it is unavailable, use Total Blocking Time
TBT is the lab metric that correlates best with INP. It is not the same measurement, but a high TBT reliably predicts a poor INP.
3
Find the long tasks
INP is usually one slow event handler, not general sluggishness. Profile the interaction that feels worst rather than the page as a whole.
4
Break up the work
Yield to the main thread between chunks, move heavy computation off it, and render the visual acknowledgement before doing the work.

What's inside

Everything this tool
does for you

INP from field data where available
Honest unavailable state, with the reason
Total Blocking Time as the lab proxy
Google’s 200ms and 500ms thresholds
Free, no signup, no daily limit

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What this tool does

INP from field data when your site has it
Total Blocking Time shown as the lab proxy that does exist
Google’s 200ms / 500ms thresholds
Explains plainly when the metric is unavailable
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