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First Input Delay (FID)

First Input Delay (FID) is a user-centric performance metric that measures the time it takes for a web page to become interactive and respond to a user's first input event, such as a click, tap, or key press. It is no longer a part of Core Web Vitals. It is replaced in March 2024 by Interaction to Next Paint (INP).

FID was considered to be one of the critical metrics for assessing a page's load responsiveness and overall user experience, as it quantifies the delay users experience when trying to interact with the page content.

FID is particularly important for pages that require user interaction, such as login forms, navigation menus, or buttons. A high FID can lead to user frustration and increased bounce rates, as users may perceive the page as slow or unresponsive. On the other hand, a web page with a low FID offers a more responsive and engaging experience, as users can interact with the page elements without encountering delays or unresponsiveness.

Google recommends aiming for an FID of 100 milliseconds or less to ensure an optimal user experience.

First Input Delay (FID)

Improving FID

To improve FID, several optimization techniques can be employed, including:

  1. Minimizing the use of render-blocking resources: Deferring the loading of non-critical CSS and JavaScript files can help reduce the time it takes for the page to become interactive.
  2. Breaking up long-running JavaScript tasks: Splitting large JavaScript tasks into smaller, asynchronous chunks can help avoid blocking the main thread and improve page responsiveness.
  3. Using browser caching: Storing frequently-used files in the user's browser cache can speed up subsequent page loads and reduce the time required for the page to become interactive.
  4. Optimizing server response times: Ensuring efficient server infrastructure and backend processing can help reduce the time it takes for the browser to receive the first byte of data, thereby improving FID.
  5. Prioritizing the loading of critical assets: Preloading or preconnecting to crucial resources, such as fonts or images, can help speed up the loading process and reduce the time to interactivity.

These are just a couple of suggestions on optimizing your FID results. Get into performance-first mindset with our comprehensive frontend performance checklist.

Monitoring and optimizing FID can be accomplished using various tools, such as Google PageSpeed Insights, Lighthouse, and Chrome User Experience Report (CrUX). These tools provide insights into FID values and offer recommendations for improving the metric.

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