INP (Interaction to Next Paint)

The Core Web Vital that measures responsiveness: how long the page takes to visually react after a user clicks, taps, or presses a key. INP watches every interaction across the entire visit and reports one of the slowest — so a page can't pass by being fast once and sluggish everywhere else. Google's thresholds: 200 milliseconds or under is good, over 500 milliseconds is poor. INP replaced the older FID metric in March 2024, and it's a much harder grader — FID only measured the delay before processing started on the first interaction; INP measures the full click-to-pixel delay on all of them. Why stores should care: shopping is interaction-dense. Add to cart, open the size selector, apply a filter, step through a gallery — every one of those is an INP event, and every one that lags reads to the shopper as a broken button. Users who click Add to Cart and see nothing happen click again, or leave. The metric feeds the page experience signal in ranking, but the conversion damage from a store that feels unresponsive usually costs more than the ranking effect does. What drags INP down on the stores we work on: heavy theme JavaScript that ties up the main thread while the user waits, plugin stacks where every installed app runs its code on every click, oversized product-variant logic recalculating the whole page on each selection, and third-party chat or tracking tags executing at interaction time. Our team profiles the slow interactions on real templates, strips or defers the code that blocks the response, and re-measures against field data until the store reacts the way a store should — instantly.