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A blank INP result in a lab speed test usually means the test did not perform a qualifying click, tap, or keyboard interaction. It can also mean the test’s observer filtered out short Event Timing entries. Scrolling and hovering do not count as INP interactions. To diagnose the right cause, check what the test did, how its observer was configured, and whether you are looking at a lab trace or real-user data.
Why does INP show no data in a lab test?
Interaction to Next Paint (INP) measures responsiveness for click, tap, and keyboard interactions during a page visit. It considers latency through the next paint and reports one of the slowest interactions, rather than averaging every interaction. If a test journey contains no qualifying interaction, there may be no INP value to report. The INP guidance from Google Chrome for Developers also identifies scrolling and hovering as gestures that INP does not measure.
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A browser automation run can load the page and still produce no INP if it never clicks, taps, or presses a key. A bot or headless-browser test without scripted interaction has the same issue. Check the recorded journey—not just whether the page loaded—to confirm that it exercised an interaction relevant to the metric.
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An empty list of event entries does not prove that no interaction occurred. By default, the Event Timing API exposes event entries only when their duration meets a 104 ms threshold. Shorter entries can therefore be filtered out. The configurable minimum threshold is 16 ms; lowering it can reveal shorter entries, though it still does not make the API report every event.
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The Custom metrics: Event Timing API guide shows how to observe buffered entries with the lower threshold:
const observer = new PerformanceObserver((list) => {
for (const entry of list.getEntries()) {
const inputDelay = entry.processingStart - entry.startTime;
const processingTime = entry.processingEnd - entry.processingStart;
const presentationDelay = entry.startTime + entry.duration - entry.processingEnd;
console.log({
name: entry.name,
duration: entry.duration,
inputDelay,
processingTime,
presentationDelay,
target: entry.target,
});
}
});
observer.observe({ type: 'event', buffered: true, durationThreshold: 16 });Also observe first-input. The INP guidance recommends it because that entry can be observed even when it is shorter than the event threshold. This can help identify a first interaction that the default filter would otherwise hide.
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What does PerformanceEventTiming.duration include?
duration is not just the time spent running an event handler. It spans from when the browser receives the event until it can paint the next frame after synchronous work initiated by the event handlers finishes. The documented duration is rounded to 8 ms for security reasons, according to Google Chrome for Developers’ Event Timing API guide.
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The other timestamps let you break a raw event entry into useful phases:
- Input delay:
processingStart - startTime—the wait before the browser can begin processing the event handlers. - Event-handler processing:
processingEnd - processingStart—the time spent running synchronous code initiated from the handlers. - Presentation delay:
startTime + duration - processingEnd—the remaining time until the next frame can be painted.
These are raw Event Timing entries, not INP scores by themselves. INP groups event-handler activity belonging to the same logical interaction, so an individual entry’s duration is not necessarily that interaction’s INP latency.
How should you troubleshoot a blank result?
- Verify the test journey. Confirm that it performs a click, tap, or keyboard action on the page. A load-only run, scroll, or hover is not enough to produce a qualifying INP interaction.
- Check the observer threshold. If you collect
evententries yourself, determine whether the default 104 ms threshold is filtering shorter entries. TrydurationThreshold: 16, the minimum configurable value, and observefirst-inputas well. - Inspect a reproduced slow interaction by phase. Use the Event Timing timestamps to distinguish input delay, event processing, and presentation delay rather than treating total duration as handler time. The lab diagnosis guide recommends CPU throttling or a lower- to mid-tier Android device to make long tasks easier to expose.
- Use field data to assess real-world responsiveness. A lab trace diagnoses only the interactions exercised in that run; it does not predict every user’s experience. The field diagnosis guide describes collecting INP and contextual details such as the interaction, its type, and when it occurred in the page lifecycle. It also describes the
web-vitalslibrary; its version 4 added deeper INP phase breakdowns and Long Animation Frames API data. Check current library version and browser support before implementation.
What does a blank lab result tell you—and what does it not?
| Measurement context | What it measures | Best use | Limitation |
|---|---|---|---|
| Lab test | Interactions deliberately simulated in the test | Reproducing and inspecting a known slow interaction in a controlled run | No qualifying scripted interaction can leave INP absent; results depend on the test journey. |
| Field measurement | Actual user interactions | Assessing responsiveness across real visits; RUM can provide interaction and page-lifecycle context | It requires field data collection and interpretation, and users’ interaction mix varies. |
INP replaced First Input Delay (FID) as a Core Web Vital on March 12, 2024. FID measured only input delay for the first interaction; INP considers interaction latency through the next paint. The date and distinction are described in Google Chrome for Developers’ announcement.
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