Name which INP phase slows your worst interaction

A button interaction feels sluggish, and Lighthouse just says my INP is bad.

IntermediateRead 5 minDoing: under an hour, once the slow interaction is already reproducible7 steps

▶ Start

What you'll have at the end

The worst interaction's slow INP phase identified, fixed, and the improved number confirmed afterward.

Before you start

You need

An interaction you can trigger by hand on demand, a click or a keypress, whose INP already comes back slow, on a page you can add a small script to.

Not covered

Tracing a slow processing number back into a UI framework's own re-render cycle, which needs that framework's own profiling tools rather than the browser's interaction-timing API alone.

Leans on

7 steps

Where to go next

Catch the React re-render hiding behind a slow INP

processingDuration turns out to be dominated by a UI framework's re-render rather than plain event-listener or vendor code

Checked 25 Aug 2026

Part of the Core Web Vitals and Performance Metrics cookbook