Interaction to Next Paint (INP)

INP replaced First Input Delay as the responsiveness Core Web Vital in March 2024. While FID only measured the first interaction, INP measures every interaction during the page visit and reports the worst one (with statistical smoothing for outliers). This gives a much more accurate picture of real-world interactivity issues.

For growth teams, poor INP directly impacts user engagement. Users who experience lag when clicking buttons, typing in forms, or interacting with dynamic content are more likely to abandon the page. Common causes of poor INP include long JavaScript tasks that block the main thread, expensive DOM manipulations triggered by user actions, and synchronous API calls during interaction handlers. Fix INP by breaking long tasks into smaller async chunks using requestAnimationFrame or scheduler.yield, debouncing expensive event handlers, using web workers for heavy computation, and optimizing React or framework rendering cycles. Chrome DevTools' Performance panel with interaction tracking helps identify which specific interactions are slow.