What is the INP metric and how to optimize it to improve site interactivity?

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The INP (Interaction to Next Paint) metric measures a page's overall responsiveness to user actions, such as mouse clicks, screen taps, or key presses. Unlike its predecessor FID, INP evaluates all interactions during the user's visit to the page and records the longest delay before a visual interface update. A low INP score causes the site to feel frozen and slow, even if it loaded quickly initially.

To optimize INP, developers need to reduce the execution time of tasks in the main JavaScript thread. Large event handlers should be broken down into smaller chunks or heavy computations should be moved to background threads using Web Workers. It is also important to avoid long macro-tasks that block the main thread and prevent the browser from rendering screen updates on time.

Consistent interface responsiveness can be achieved through the following practical steps:

1. Analyze the Performance tab in developer tools to find long event handlers and functions with high execution time.
2. Use asynchronous code execution and task-splitting functions to give the browser an opportunity to process user input between animation frames.
3. Minimize the number of simultaneous DOM tree modifications and avoid forced synchronous layout recalculations immediately after style modifications.
4. Postpone the initialization of non-essential libraries and widgets until after the initial page load and complete interface hydration are finished.

Implementing these measures will significantly reduce response latency, make the web application more dynamic and comfortable for users, and improve overall Core Web Vitals scores, which will positively impact the site's search engine rankings.

What is the INP metric and how to optimize it to improve site interactivity?

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