First Input Delay (FID) vs. Interaction to Next Paint (INP)

In March 2024, the Interaction to Next Paint (INP) will replace the First Input Delay (FID) as a new Core Web Vital. FID measures the time between a user's first interaction with a webpage and when the browser starts processing the interaction event. Whereas, INP measures the interaction event's entire lifespan, including processing event handlers, recalculating layouts, and painting updates to the screen. In addition, INP considers a broader range of performance factors, thereby enhancing the user experience. Tools to measure INP are available, and optimizing for INP can be achieved using more efficient JavaScript, effective event handlers, and similar tactics.