First Input delay (FID) is an essential performance metric that Google uses to measure a website’s PageSpeed performance. 

When it comes to a website’s success, delivering a fast-loading website is crucial. But how do you determine if your website’s PageSpeed performance is fast or not? Here’s the First Input Delay that comes into the picture along with the other performance metrics. 

Let’s understand about the First Input Delay (FID) metric and explore the powerful strategies to optimize the FID in order to improve the Google PageSpeed score. 

Note: Google developed and launched a new metric Interaction to Next Paint (INP) to replace the FID metric in March 2024.  

What Is The First Input Delay?

Google developed the First Input Delay to measure a web page’s responsiveness. In simple words, the First Input Delay (FID) calculates the span of time from when a visitor first interacts with the web page to when the web page starts giving the response. This is also known as input latency.

Let’s understand with an example. Assume you click on a link after opening a web page. FID measures the time between clicking that link and the time when the browser starts responding to it. This First Input Delay is measured in milliseconds (ms).  

The Difference Between FID And INP

To better understand PageSpeed performance, Google replaced the First input Delay with a new metric: Interaction to Next paint (INP). But how does INP differ from the FID?

Let’s explore how the First Input Delay (FID) differs from the Interaction to Next Paint (INP). 

The Top Helpful Tools To Measure The First Input Delay

Here, we will see the most helpful tools to measure the First Input Delay (FID) of your website.

• Google PageSpeed Insights

Google developed an online tool, Google PageSpeed Insights to analyze the performance of core web vitals and provide a PageSpeed score based on a few key performance metrics.

To measure the First input Delay (FID), you need to enter your website’s URL and click on the analyze button and you would see the FID along with various other important metrics.

Along with your FID score, PageSpeed insight would also suggest improvements to get your websites a good FID value & pass the Core Web Vitals.

• GTmetrix

GTmetrix is the best alternative tool to measure the performance of the core web vitals. This online tool allows you to customize your test location ,device, network connection, and browser.

What Is A Good FID Time?

Google sets threshold values for each performance metric to categorize performance. Let’s examine the threshold values of FID metrics. 

• If the FID value is less than 100 ms, Google considers this a good FID time and marks it in green.

• A FID time between 100 ms and 300 ms indicates that it needs to be reduced to pass the core web vitals test. Google marks it in orange.
• If the FID time exceeds 300 ms, your website failed the core web vitals assessment, and Google will mark it in red. 

How To Improve FID Performance?

At this point, you are aware of a good FID time. If your website’s FID time is more than 100 ms, you need to optimize your First Input Delay to achieve a good PageSpeed score and enhance the user experience by improving your website’s performance.  

Let’s see how you can improve the FID performance using your technical skills only, it might take a little time & needs some technical skills. We will also see how you can do this within a few minutes just by installing RabbitLoader.

Minimize main thread work /Break up the long tasks

Breaking up the JavaScript code is one of the most effective ways to improve your website’s FID time. In such cases, you need to identify the long tasks that increase the FID time by blocking the main thread. Then you must split them into smaller tasks. It can minimize your main thread also. 

By allowing multi-threading, which means that if the main thread is busy with critical tasks, some non critical tasks could be moved to the web workers. This would need a very specialized set of skills to be able to implement it on your website.

Check more: Minimize main thread work

Whereas, RabbitLoader implements multi-threading and optimizes your website for the perfect FID value without needing you to write a single line of code.

Compressing and minifying CSS and JavaScript files

The loading speed of a website can also depend on the page size. In your CSS and JavaScript file, many characters such as line breaks, and comments are present which unnecessarily increases the page size for the browser, slowing down the loading speed.

Compression and minification are the best ways to mitigate this issue. Manually removing these unnecessary characters from your CSS and JavaScript file might need a lot of time and effort especially if the website has a lot of CSS codes.

When using RabbitLoader, you don’t need to put any extra for this. Along with the other optimization techniques, RabbitLoader also takes care of this. For more details on resource minification, please checkout our Minify Resources blog. 

Defer the JavaScript functions 

During the page rendering, in general, the browser loads every resource. This would increase the loading time. You can improve the loading time by deferring the JavaScript functions which are not required for the initial loading time. This can be achieved by adding a syntax like the below example,

Syntax: <script src="https://www.domain.com/file.js" defer></script>  

If you are technically sound, you can easily defer your non-critical JavaScript functions, but if you are not from a technical background, the best way to optimize FID is to install RabbitLoader.

Final Thoughts  

Even though Google replaced this FID with INP, Google PageSpeed still shows the FID metric on its tests. When you work on improving FID, your INP time will also be improved. So, if you are struggling with a poor FID score, you need to implement the above strategies. 

Whether you do it manually or using an optimization tool like RabbitLoader it is up to you.If you want an effortless solution, optimize your FID performance with RabbitLoader.