INP (Interaction to Next Paint) is a Core Web Vitals metric that measures the longest delay between any user interaction—click, tap, or keypress—and the next visible update on screen. Google considers a score under 200ms good, 200–500ms needs improvement, and above 500ms poor.
INP (Interaction to Next Paint) in plain English
INP measures how quickly a webpage visually responds to user input. Every click, tap, and keystroke on a page is tracked, and INP reports the worst-performing interaction from the entire visit. For example, when a shopper clicks 'Add to Cart' and the button appears frozen for 400ms before anything changes, that delay is recorded as a candidate for the page's INP score.
Mechanically, INP captures the time from the moment an input event is received to the moment the browser completes the next paint that reflects a response to that input. This window encompasses three phases: input delay (time before the browser begins processing the event), processing time (time to run the associated JavaScript handlers), and presentation delay (time for the browser to render and paint the updated frame). A high INP score signals that at least one of these phases is consuming excessive time, typically due to long JavaScript tasks blocking the main thread.
A store with a well-optimized INP score delivers immediate visual feedback on every interaction—filter selections update the product grid instantly, quantity steppers respond on the first tap, and checkout form fields register keystrokes without lag. A store with a poor INP score exhibits the opposite: users click buttons that appear unresponsive, double-tap because nothing happened, or abandon the interaction entirely. The difference is not subtle to shoppers, even when they cannot name the technical cause.
Google's thresholds for INP are 200ms or under (good), 201–500ms (needs improvement), and above 500ms (poor). On ecommerce pages, the interactions most likely to inflate INP are faceted filtering, cart drawer animations, and address autocomplete fields—all JavaScript-heavy interactions that fire on high-traffic, high-intent pages. Ecommerce operators measuring INP in field data via Chrome User Experience Report (CrUX) see the metric reflect real customer sessions, not synthetic lab conditions, making it a direct signal of actual shopper experience.
Why inp (interaction to next paint) matters for ecommerce
For ecommerce stores, INP is the metric most directly tied to the moment a shopper decides whether to keep engaging or leave. A sluggish 'Add to Cart' button, a filter that freezes the product grid, or a checkout field that lags behind keystrokes all register as high INP. These friction points appear at the highest-intent moments in the purchase funnel. Google also uses Core Web Vitals, including INP, as a ranking signal, meaning a poor score carries both a conversion cost and an organic visibility cost simultaneously.