Interaction to Next Paint

Interaction to Next Paint, usually shortened to INP, is a performance metric that measures how quickly a web page visually responds after a user interacts with it. Every time a visitor taps a button, clicks a link, or types into a form, the browser needs to process that input and update what appears on screen. INP captures the delay between the interaction and the moment the browser paints the next visual change, then reports a single value that represents the worst, or near-worst, response a user experienced across an entire visit. A lower number means the page feels snappy and responsive, while a high number signals sluggishness that frustrates people and pushes them to leave.

Mechanically, INP works by observing all the qualifying interactions during a page session, such as clicks, taps, and key presses. For each one, the browser measures three phases: the input delay before event handlers begin, the processing time while scripts run, and the presentation delay before the next frame is painted. The full duration of the slowest interaction, roughly, becomes the reported score. This differs from older measurements that only looked at the very first input a user made. Because INP watches the entire visit, it exposes problems that appear deep into a session, like a heavy filter on a product page or a menu that stalls when JavaScript is busy. Long tasks that block the main thread are the usual culprits, since the browser cannot respond to input while it is occupied with other work.

The term comes from combining the idea of an interaction with the browser painting its response to the screen. Google introduced Interaction to Next Paint in 2023 as an experimental metric and promoted it to a Core Web Vital in March 2024, where it replaced First Input Delay. That change reflected a desire to measure real responsiveness throughout a session rather than only the opening moment, since the first click often happens before heavy scripts have loaded and does not represent the true experience.

For a business, INP matters because responsiveness shapes how people perceive quality and trust. A store where the add-to-cart button lags, or a form that freezes after a keystroke, quietly erodes conversions even when the design looks polished. Since INP is a Core Web Vital, it also feeds into how Google evaluates page experience, so poor scores can weigh on rankings alongside the direct harm to user behavior. Sites that respond within a couple hundred milliseconds tend to feel effortless, while delays approaching half a second or more read as broken.

Common mistakes include treating INP as a loading problem when it is really about ongoing interactivity, and shipping large bundles of JavaScript that tie up the main thread. Teams sometimes optimize the initial paint, watch Largest Contentful Paint improve, and assume responsiveness is handled, only to find that third-party scripts and unoptimized event handlers still create jank. Breaking work into smaller tasks, deferring nonessential scripts, and avoiding layout thrash all help. INP sits alongside Largest Contentful Paint and Cumulative Layout Shift as one of the three Core Web Vitals, and render-blocking resources that slow the whole experience often hurt several of these metrics at once, which is why performance work rewards a holistic approach rather than chasing one number in isolation.