FID vs. INP: Navigating the Evolution

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FID and INP are two terms that have been more well-known in the context of website performance optimization in recent years. Two key metrics that have gained significant importance in recent years are First Input Delay (FID) and Interaction to Next Paint (INP). 

When it comes to online performance, these measurements are essential for comprehending and enhancing user experience.

Understanding FID

First Input Delay (FID) is a key user-centric performance indicator that gauges how long it takes the browser to react to a user’s initial input on a webpage. Simply put, it measures the amount of time that passes between a user’s interaction with a page (such as clicking a button or link) and the browser’s start of processing such interaction.

Since it directly affects how users perceive a website’s responsiveness and engagement, FID is extremely significant. Users may become frustrated with a high FID, which could raise bounce rates and decrease engagement.

Factors Influencing FID


  1. JavaScript Execution: Heavy JavaScript execution can significantly delay the browser’s response to user input.
  2. Main Thread Activity: When the main thread is busy executing tasks, such as rendering large elements or processing JavaScript, it may delay responding to user input.
  3. Network Latency: Slow network connections can prolong the time it takes for user input to reach the server and receive a response.

Measuring FID

Typically, Web Vitals and Google’s Lighthouse, which offer insights into a variety of web performance factors, are used to measure FID. It is expressed in milliseconds (ms), where higher performance is indicated by lower values.

First Input Delay Shortcomings

FID ignores all future interactions that might be just as sluggish as or even slower, simply taking into account the delay of the initial input event.

It also does not assess other elements that may contribute to a longer visual feedback lag between user events. 

This encompasses the duration required to handle event handlers and update the layout before presenting the user with visual feedback.

Optimizing FID

To improve FID and enhance user experience, consider the following strategies:

  1. Minimize JavaScript Execution: Optimize JavaScript code by eliminating unnecessary scripts and reducing their size.
  2. Prioritize Critical Rendering Path: Ensure that critical resources are loaded and rendered quickly to minimize main thread activity.
  3. Use Browser Caching: Leverage browser caching to store frequently accessed resources locally, reducing network latency.
  4. Implement Code Splitting: Divide large JavaScript bundles into smaller, more manageable chunks to minimize parsing and execution time.
  5. Asynchronous Loading: Load non-essential JavaScript asynchronously to prevent it from blocking the main thread.

By implementing these strategies, you can significantly reduce FID and improve overall user experience on your website.

Understanding INP

Google introduced Interaction to Next Paint (INP), a relatively new statistic, to accompany FID. It calculates how long it takes for a user input event—such as clicking a button or pressing a link—to cause a web page to become graphically interactive.

While FID merely measures the input delay—the interval of time between user input and the browser’s commencement of the event handler—, INP measures the time it takes the browser to process the event handlers is known as the processing delay.

It also takes into account the amount of time it takes the browser to update the layout and apply the pixels on the screen.

INP is concerned with a website’s ability to adapt visually to user input. INP assesses how rapidly the page modifies its visual state in response to user interaction.

INP is important as it has a direct bearing on ergonomics and user comfort. User fatigue and discomfort can result from exerting too much pressure when interacting with input devices, which eventually lowers engagement and reduces usability.

Factors Influencing INP


  • Input Device Design: The design of input devices, such as keyboards and touchscreens, can influence the amount of pressure required for interaction.
  • Material Quality: The quality of materials used in input devices can affect their responsiveness and the pressure required for input.
  • Interface Design: Poor interface design, such as small or poorly positioned interactive elements, can increase the pressure users need to apply.

Measuring INP:

With the use of specialized tools made to measure the pressure exerted on input devices during user engagement, INP can be determined. After that, this data can be examined to pinpoint areas where interface layout and device design need to be improved.

Optimizing INP

To optimize INP and enhance user comfort, consider the following strategies:

  • Ergonomic Design: Design input devices with ergonomics in mind, ensuring that they fit comfortably in the user’s hand and require minimal pressure for interaction.
  • Material Selection: Use high-quality materials that offer a balance of responsiveness and durability, reducing the pressure required for input.
  • Interface Optimization: Optimize interface design to ensure that interactive elements are appropriately sized and positioned for easy access, minimizing the pressure users need to apply.

By prioritizing user comfort and ergonomics, you can improve INP and create a more enjoyable and accessible user experience.

Navigating the Evolution of FID and INP

The development of FID and INP is a reflection of how web performance optimization objectives are changing. Page load speed and other traditional measures are no longer adequate to adequately measure user experience as websites grow more dynamic and engaging. By emphasizing user-centric measures that have a direct bearing on engagement and retention, FID and INP close this gap.

To effectively optimize FID and INP, digital marketers and web developers must adopt a holistic approach to performance optimization. This approach involves:

  • Prioritizing User Experience: Putting the needs and preferences of users at the forefront of optimization efforts.
  • Streamlining Critical Rendering Path: Optimizing rendering processes to minimize delays in both input responsiveness and visual updates.
  • Minimizing Third-Party Impact: Balancing the inclusion of third-party scripts with their potential impact on FID and INP.
  • Continuous Monitoring and Iteration: Regularly monitoring performance metrics and iterating on optimization strategies to maintain peak performance.

In conclusion, First Input Delay (FID) and Interaction to Next Paint (INP) are indispensable metrics in the world of web performance optimization. By focusing on user-centric measures of responsiveness and interactivity, FID and INP provide valuable insights into the user experience landscape.

In the ever-changing landscape of digital marketing, North Rose Technologies embraces the evolution of FID and INP and understands it to be a strategic imperative for success.

Frequently Asked Questions

  • How do FID and INP impact user experience?

    FID and INP directly impact user experience by influencing the perceived responsiveness and interactivity of a website.

  • What factors affect FID and INP?

    Several factors can impact FID and INP, including JavaScript execution, main thread activity, rendering performance, and resource loading.

  • What are some strategies for optimizing FID and INP?

    To optimize FID and INP, consider prioritizing user experience, streamlining the critical rendering path, and minimizing third-party impact.