The Hidden Impact of Third-Party Scripts on INP (Core Web Vitals)

INP replaced FID because users care about every interaction, not just the first. That means late-loading tags can still tank your score.

Analytics scripts often run on every route. The more tags you add, the more long tasks show up around interactions.

If you want fast conversion flows, you have to budget your main-thread time the same way you budget bundle size.

A click triggers JS handlers, style recalculation, and layout. If a tag runs during that window, INP spikes.

const observer = new PerformanceObserver((list) => {
  for (const entry of list.getEntries()) {
    if (entry.entryType === "event") {
      const interaction = entry as PerformanceEventTiming
      console.log(interaction.name, interaction.duration)
    }
  }
})
observer.observe({
  type: "event",
  buffered: true,
  durationThreshold: 40,
})

Use this kind of instrumentation to spot the exact handlers that compete with analytics execution.

• List every third-party tag and map it to a business owner.
• Measure INP before and after removing each tag in staging.
• Keep only tags that directly influence revenue or compliance.

AnonView's collector avoids dynamic imports and large runtime dependencies. It captures intent signals and sends only minimal metadata.

• Keep analytics scripts under 5 KB compressed when possible.
• Avoid synchronous trackers on interaction-heavy routes.
• Use a relay to strip transport metadata and limit payload size.