Unlock the Secrets of First Input Delay: Your Ultimate Performance Metric Glossary Page

As a website owner or developer, you may have heard the term First Input Delay (FID) in the context of website performance. 

FID is a performance metric that measures the time it takes for a user's first interaction with a website to be processed by the browser. In this article, we will explore what FID is, how to measure it, and how to improve it. 

What is First Input Delay?

First Input Delay (FID) is a performance metric that measures the time it takes for a user's first interaction with a website to be processed by the browser. This interaction could be clicking a link, tapping a button, or entering text into a form field. FID measures the time between the user's action and the browser's response. 

FID is an important metric because it measures the interactivity of a website. A website with a high FID will feel slow and unresponsive to users, while a website with a low FID will feel fast and responsive.

Why is First Input Delay So Important?

The reason why FID is a crucial metric is because it directly impacts user experience. A high FID score can lead to frustration, confusion and decreased engagement, which can result in higher bounce rates, lower conversions, and negative reviews. On the other hand, a low FID score can lead to a better user experience, increased engagement, and potentially higher conversions.

To optimise FID, it is important to reduce the amount of work that the browser has to do before it can respond to user input. This can be achieved through techniques such as code splitting and lazy loading, which we mentioned earlier.

Additionally, it is important to minimise the use of JavaScript that blocks the main thread, as this can lead to delays in processing user input. It's recommended to use web workers to offload CPU-intensive tasks to a separate thread, thus freeing up the main thread to process user input more quickly.

How to Measure First Input Delay

FID can be measured with a First Input Delay Test using tools like Google's PageSpeed Insights, Lighthouse, or Chrome User Experience Report (CrUX). These tools provide a FID score, which represents the percentage of page loads with a FID of 100 milliseconds or less.

To improve FID, it is important to understand the factors that contribute to a high FID score. These factors include server response time, JavaScript execution time, and the main thread blocking time. 

Max Potential First Input Delay

Max Potential First Input Delay (Max FID) is another performance metric that measures the worst-case scenario for FID. Max FID measures the time it takes for the longest task on the main thread to complete, which is the task that blocks user input.

Max FID is an important metric because it measures the maximum delay that users may experience when interacting with your website. To improve Max FID, you can use the same techniques used to improve FID, such as optimizing server response time, reducing JavaScript execution time, and minimizing main thread blocking time. 

How First Input Delay Impacts Google Searches 

Google uses FID as one of the Core Web Vitals, a set of performance metrics that it considers important for delivering a good user experience. Starting in May 2021, Google began using Core Web Vitals as a ranking factor for search results on mobile devices. 

As a website owner or developer, it is important to optimize FID and other Core Web Vitals to ensure that your website ranks well in Google search results. By optimizing FID, you can improve the interactivity of your website, which will lead to a better user experience and higher engagement. 

First Input Delay Core Web Vitals

Core Web Vitals are an important set of performance metrics that measure the user experience of a website. In addition to FID, Core Web Vitals also include: 

• Largest Contentful Paint (LCP) measures the time it takes for the largest content element on a page to become visible. This could be an image, video, or block of text. LCP is an important metric because it measures the time it takes for users to see meaningful content on a page, which can impact user engagement and bounce rates.
• Cumulative Layout Shift (CLS) measures the amount of unexpected layout shifts that occur during page load. This metric is important because unexpected layout shifts can be frustrating for users, especially if they are trying to interact with a page. CLS is calculated by measuring the area of a page that is impacted by layout shifts and the distance that the impacted elements move. 

How to Improve First Input Delay 

To improve FID, you can follow these steps:

• Optimize server response time: An effective way to achieve this is by using a content delivery network (CDN). A CDN distributes your website's content across multiple servers, enabling faster access to the content for users around the world.
  
  By reducing the distance between users and the server, a CDN can significantly improve your website's First Input Delay (FID), which is a crucial metric for user experience. Overall, using a CDN is an excellent strategy to optimize your website's performance and improve user satisfaction.
  
  
• Reduce JavaScript execution time: One way to achieve this is by using code splitting, which involves loading only the necessary JavaScript code for each page. This can help decrease the time it takes for the page to load and become interactive. Additionally, using lazy loading can defer the loading of non-critical JavaScript code until it is needed, further reducing the initial page load time. 
  
  

• Minimize main thread blocking time: Code splitting and lazy loading techniques can help reduce the amount of JavaScript code that needs to be executed on the main thread, which can result in faster page load times and a better user experience.
  
  

• Code splitting is a technique for optimizing website performance by dividing a large JavaScript file into smaller chunks that can be loaded separately. This allows the browser to load only the necessary code for a particular page, reducing the initial page load time and improving performance.
  
  By loading only the code required for each page, code splitting can also reduce the amount of unused code that is downloaded and executed, further improving performance.
  
  

• Lazy loading defers the loading of non-critical resources, such as images or JavaScript files, until they are needed. By delaying the loading of these resources until the user interacts with the page, lazy loading can significantly reduce the initial page load time, resulting in a better user experience. For example, if a user doesn't scroll down a page, there's no need to load images or JavaScript that are further down the page.

Additionally, using web workers to offload CPU-intensive tasks to a separate thread can further reduce the main thread blocking time, allowing the browser to respond more quickly to user input.

Web workers are a way to execute JavaScript code in a separate thread, allowing CPU-intensive tasks to be offloaded from the main thread. By executing code in a separate thread, web workers can reduce the main thread blocking time, resulting in a more responsive and faster website. This is particularly useful for applications that perform complex calculations or heavy processing, such as video or audio manipulation, which can be offloaded to a separate thread for faster execution.

• Test and Monitor FID: To monitor your website's FID score and identify areas for improvement, you can use tools like Google's PageSpeed Insights, Lighthouse, or Chrome User Experience Report (CrUX). These tools provide insights into your website's performance, including FID score, and offer recommendations for improving website speed and user experience.
  
  By regularly monitoring your website's FID score, you can identify any issues that may be impacting user experience and take steps to improve website performance, resulting in a better user experience and potentially higher engagement and conversions. 

A high FID score can lead to a slow and unresponsive website, which can result in lower engagement and a poor user experience. On the other hand, a low FID score can lead to a fast and responsive website, which can result in higher engagement and a better user experience. Ask us how we can improve your FID score today. 

Improve Your Core Web Vitals Today 

By following these steps and monitoring your FID score using tools like Google's PageSpeed Insights, Lighthouse, or Chrome User Experience Report (CrUX), you can ensure that your website provides a good user experience and ranks well in Google search results. 

At Fix My Site Speed, we specialize in optimizing website performance, including FID. If you need help improving your website's FID score or other performance metrics, please contact us today. We’d be happy to help you improve your website's speed and user experience.