Interaction to Next Paint (INP)
Interaction to Next Paint (INP) measures a page's responsiveness by observing the latency of every click, tap, and key press during a visit and reporting a representative high value — close to the worst. Latency spans from the input to the next frame the browser paints. INP became a Core Web Vital in March 2024, replacing First Input Delay, because it captures the full processing-plus-render cost across all interactions, not just the delay of the first one.
What this means
INP observes the latency of all qualifying interactions during a page visit and reports a single value near the worst (discarding a few outliers on pages with many interactions). Each interaction's latency runs from when the user acts to when the browser paints the next frame reflecting the result.
Why it replaced FID
First Input Delay only measured the input delay of the first interaction and stopped before event processing and rendering. INP, which became a stable Core Web Vital in March 2024, measures the entire input-to-paint duration across every interaction, giving a fuller picture of how responsive the page feels throughout the visit.
- INP = representative worst interaction latency
- Latency = input → processing → next paint
- Replaced First Input Delay as a Core Web Vital in 2024
Why it misleads
INP reflects only pages that were interacted with, so a page with no interactions has no INP. A single slow interaction can dominate, and the value depends on device speed — slow phones expose blocking tasks that fast laptops hide. Read it in the field across real devices.
How it appears in analytics and logs
A high INP means at least one common interaction was slow to produce a visible change — usually long JavaScript tasks blocking the main thread between input and paint.
Diagnostic use case
Use INP to find pages that feel sluggish to use after they load, since it surfaces the interactions where long tasks blocked the main thread and delayed the visible response.
What WebmasterID can help detect
WebmasterID can record interaction-timing events first-party so INP is read against human-classified sessions rather than scripted automation.
Common mistakes
- Comparing INP to old FID numbers as if they measured the same thing.
- Testing INP on fast hardware that masks main-thread blocking.
- Ignoring that pages without interactions report no INP.
Privacy and accuracy notes
INP is an interaction-latency measurement from the browser, not personal data. This is educational, not legal advice.
Related pages
- Total Blocking Time (TBT)
Total Blocking Time (TBT) measures how long the main thread was blocked between First Contentful Paint and Time to Interactive. For each task longer than 50 milliseconds, the portion above 50ms counts as blocking time, and TBT is the sum of those portions. It is a lab metric — Lighthouse reports it — and web.dev treats it as a proxy for field responsiveness because high TBT usually predicts a poor Interaction to Next Paint.
- Largest Contentful Paint (LCP)
Largest Contentful Paint (LCP) reports the render time of the largest image or text block visible in the viewport, measured from when the page starts loading. It is one of Google's Core Web Vitals, exposed through the Largest Contentful Paint API, and the candidate element can change as larger content paints — the final value is taken at the last candidate before user interaction. web.dev breaks LCP into TTFB, resource load delay, load duration, and render delay to localise the bottleneck.
- Cumulative Layout Shift (CLS)
Cumulative Layout Shift (CLS) measures the largest burst of unexpected layout shifts during a page's lifetime. Each shift contributes a layout-shift score equal to the impact fraction times the distance fraction, and the Layout Instability API reports those entries. To avoid penalising long-lived pages, CLS is the maximum sum within a session window of shifts rather than a running total, which is why a stable page that occasionally moves can still score low.
- Website observability
Responsiveness signals beside traffic.
Sources and verification notes
Last reviewed 2026-06-24. Facts are checked against primary/official sources where available; uncertain specifics are marked “Data not yet verified” rather than guessed.