What is First Input Delay? Understanding Google’s Core Web Vitals Elementary

One of Google’s newest ranking factors rolling out in 2021 is Core Web Vitals looks at three different metrics that try to analyze and understand something about your website’s user experience. Let’s talk about one of those metrics in this article today First Input Delay.

This image shows the FID measurement Thresholds.

What is First Input Delay?

First Input Delay is the time it takes from when a user first interacts with your page that is when they clicked on a link tapped on a button did something to interact with your web page how long it takes from when the user first interacts to the time when the browser is able to respond to that interaction we can think of FID as measuring how quickly the website can be interacted with by a visitor so if somebody comes to your website how quickly does your website let that person interact.

Key Question to address: is if the website responds to an interaction like a click or a tap in under 100 milliseconds?

What Causes Poor FID?

Poor FID is caused by excessive main thread work the main thread of your website can be thought of like a line at a store if you’re the 25th person in line you’re going to be waiting a while, If you’re only the second person in line you’re not going to be waiting quite as long and so that line on your website or the thread on your website if it’s full of a lot of other requests and then and your user comes along and tries to click on a link well now they’re the last person in that line and they’re potentially going to be waiting a while. On a website that main thread can be full of lots of requests 

  1. Third-party scripts
  2. Large JavaScript files with long execution times
  3. Too many HTTP requests

So as you think about your FID score and wanting to improve this you want to make sure that you’re making your WordPress website idler, reducing how busy your website is so that way your website can respond more quickly when people try to interact with it.

FID Measurement Thresholds

There are three different categories for FID measurements

  1. Good: Good means that your website is responding to people’s interactions within hundred milliseconds.
  2. Need improvement: means your website is responding in more than 00 milliseconds, but less than 300 milliseconds.
  3. Poor: where your website takes longer than 300 milliseconds to respond the 100 milliseconds timing might seem ridiculously fast but it is not arbitrary at 100 milliseconds something feels instantaneous we don’t even notice that there was any kind of delay at 100 milliseconds, between 100 milliseconds to 300 milliseconds or brains do start to perceive that there was a little bit of a lag there was a little bit of a delay happening there after 300 seconds we really do start to notice the delay and things start to feel slower even at a subconscious level so by making your website respond to people interactions in less than 100 milliseconds your website will feel instantaneous will feel that much faster it’ll be that much better for people when they’re using your website.

What if a user doesn’t interact?

  1. Some visitors won’t interact with your website: What if people don’t interact with your website some people who visit your website won’t interact with it at all, of course, it’s not just people who don’t interact right there are different ways that people can interact with your website.
  2. Some visitors will try to interact when your website is busy, resulting in a higher FID: some people are going to try and interact with your website when it’s really busy when your website is trying to load a whole bunch of other stuff that’s going to result in a much higher FID
  3. Some visitors will try to interact when your website is idle, resulting in a lower FID: some people who come to your website at the best possible time your website is idle, it’s not trying to load anything else and that’s when somebody clicks on a link or taps on a button and in that state, you’re going to get a lower FID because your website is going to be able to respond right away. So because of these differences and how people interact. 
  4. Google is aggregating FID scores and wants 75% of visitors to have a “good” value or better.

So you don’t need to aim for everybody to have an FID of less than 100 milliseconds; you want to aim for 75 percent of your visitors to have an FID or less than 100 milliseconds that does present a problem though when it comes time to measure FID.

Total Blocking Time Is An Alternative

This image shows the all about total blocking time.

FID can’t be measured in a lab because it needs to measure actual interactions requested by actual people visiting your website. You can’t replicate that in a lab setting so an alternative lab test can measure a similar metric of total blocking time. Total blocking time is definitely different from the first input delay but they both kind of get at the same idea and optimizing FID also optimizes total blocking time. So with that in mind let’s talk about how we know if we have an FID issue

How do you know if you have an FID issue?

There are a few different tools out there that you can use to measure ID and total blocking time.

  1. PageSpeed Insights: which measures both FID and total blocking time.
  2. Google Search Console’s Core Web Vitals report: which measures FID only.
  3. WebPage test: which measures total blocking time only    

Main Takeaway

Make sure your website can respond within 100 ms when visitors interact with things like buttons, links, and navigation. This is especially important in the first interaction.

You can also read about: What is Cumulative Layout Shift (CLS)? Understanding Google’s Core Web Vital Elementary.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s