 I'm about to launch my new site, and I get a report of a major INP problem. I don't know what the issue is, I only have a URL, and I need to fix now. To start, let's interact like a user and measure how the page performs using the DevTools performance panel. Poor INP most often happens on mobile, so turn on mobile display emulation. Now here's a vital step. I'm running this page on a desktop machine on Wi-Fi, but I want to know what it's like on a slower mobile device, so turn on mid-tier mobile throttling. This hamburger menu is a good place to start. To record, click the hamburger button and stop recording. Now here's a view of all the pages' activity for that interaction. First, expand the interactions track, which marks the time from when I clicked to when a response was shown on screen. The interaction is lined up with the main thread activity, so we can see what was taking so long, these long tasks. The call stack shows the click event calling my listener, unhelpfully renamed I by my build step. So what's it doing? Down in the summary pane is a link to the page source. Clicking through, I can see the code causing the slow interaction, and now I can start fixing it.