What is the First Input Delay for SEO?

First Input Delay for SEO

Written by Jeremy Earle, JD

March 17, 2022

Learn what First Input Delay (FID) is, what causes it, and how to fix it in this Core Web Vitals metric’s performance.

Google considers First Input Delay (FID) a small ranking factor for user experience.

This article provides an easy-to-understand introduction to FID to make sense of the subject.

Google isn’t the only one annoyed by a delay in the first input. Increasing sales, ad revenue, and lead generation is facilitated by optimizing the site’s performance.

Delay in first data input is called “first input delay.”

This is a way to track how quickly a visitor may interact with a site while it is still loading, and it is called FID. Input Latency is a term for this.

The act of pressing a button, clicking a link, or entering a keystroke is an interaction. Other types of interaction points, such as text input fields, dropdowns, and checkboxes, will be measured by FID.

Because no reaction is expected from the site, actions like scrolling or zooming are not considered interactions.

FID’s purpose is to test how quickly a site responds while loading.


Images and scripts that download non-orderly fashion are the most common source of First Input Delay.

Disorganized programming causes the web page download to repeatedly stop and start, then stop again. This results in a lack of responsiveness when users interact with the website.

When there are no traffic signals, it’s like being stuck in traffic congestion. Bringing order to the traffic is an important part of fixing the situation.

This is how Google explains why there is an input delay:

Because the browser’s main thread is occupied with other tasks, it cannot respond to the user’s input. This is known as input latency.”

Your app is loading a huge JavaScript file, which causes the browser to get overburdened.

As long as it’s doing that, the JavaScript it’s loading might tell it to do something different,” he says.


First Input Delay is a result of scripts and images being provided to the browser in an unorganized fashion during download; hence the solution to this issue is to carefully organize the download process.

Using HTML elements to manage how scripts are downloaded, optimizing graphics (HTML and images), and carefully removing superfluous scripts are the most common solutions to the problem of FID.

The goal is to optimize what is downloaded to avoid the traditional pause-and-start downloading of unstructured web pages.


To display a web page, browsers are software that performs the necessary operations. Scripts, pictures, fonts, and other design elements must be downloaded, and they must be run (executed) before the web page can be built by the HTML instructions.

Rendering is the name given to this procedure. When a browser puts together the HTML code and graphics to create a web page, it does what the word “render” means: making something.

“Threads” are shorthand for “threads of execution” and are used to refer to the different rendering processes. This refers to a specific series of events (in this case, the many individual tasks done to render a web page).

One thread, known as the “Main Thread,” is responsible for generating (rendering) the page a user sees on a browser’s screen.

The main thread shows the graphics and scripts that are downloaded and executed when a person views a website as cars on a highway.

Some code is huge and takes a long time to run. Therefore, other jobs are put on hold while they wait for the lengthy and cumbersome code to exit the freeway (finish downloading and executing).

Code the web page so that it downloads as quickly as feasible by prioritizing which code is downloaded first and when it gets executed.


Core Web Vitals and First Input Delay are two areas where you’ll find you can’t do anything about the underlying code. For your rivals, this is also likely the case.

Consider the case when your firm relies on Google AdSense (a large render-blocking script), in which case the situation will be the same for your competition. Lazy loading and Google Ad Manager can be helpful solutions.

In some circumstances, the best you can do in the circumstances may suffice because your competitors may be doing the same.

Take your victories wherever you can find them in those situations. Don’t worry about the losses you can’t control.


In a way, JavaScript is like a little engine that drives things forward. JavaScript may be used to ensure that both the first and last names are entered on a form.

A popup thank you message may be spawned when a button is touched using JavaScript.

The problem is that it has to be downloaded and then run (execute) when it comes to JavaScript. So they are two things that contribute to input latency.

If there is a large JavaScript file at the top of the page, it will prevent the remainder of the page from rendering (visible and interactive) until the script has finished downloading and executing.

This is known as page blocking.

These scripts should be relocated so they don’t interfere with other page elements awaiting their turn to begin rendering.

This can be an issue when placed at the end of an extremely long web page.

There will still be a download signal from your browser when you are ready to engage with the enormous page, so be aware of that (because the big JavaScript file is lagging at the end). It is possible that the website will download faster but will subsequently stall while waiting for JavaScript to run.

That problem can be solved!

Async and deferred attributes are listed here.

The Defer and Async HTML elements are like traffic lights that govern the start and stop of JavaScript downloads and executions.

When an HTML attribute is applied to an HTML element, it alters or enhances the element’s functionality in some way.

When you learn a new talent, it becomes a part of your identity.

In this scenario, the Defer and Async properties instruct the browser to allow HTML processing to continue while the file is being downloaded. These characteristics instruct the browser to keep the main thread running while downloading JavaScript.

Attribute of Async

JavaScript files with the Async attribute will download and then run as soon as they have been saved to the user’s computer. The JavaScript file stops the main thread when it begins to run.

When a file begins to download, it normally blocks the main thread. As an alternative, you can use an async attribute instead.

If you’re downloading anything, that doesn’t have to wait for the main thread.

Third-party JavaScript files, such as advertising and social sharing, benefit from the async feature because the order in which they are executed does not matter.

The Attribute Deferral option is available.

Deferred JavaScript files will be downloaded asynchronously as well.

JavaScript will only begin to run when the page has been downloaded and displayed. Web page scripts, including deferred scripts, run in the order they appear on the page.

It is useful for JavaScript files that depend on page components loading and when the order they are run is critical.

The deferred property should be used whenever a script isn’t necessary to the page’s display.


First Input Delay scores might vary and be inconsistent; thus, it’s vital to be aware of this. The scores are different for each visitor.

Because the score is based on a person’s unique interactions with a site, this fluctuation is inevitable.

Some visitors may not engage until all of the assets are loaded and ready for use.

According to Google, the following is what it means:

It’s unlikely that every time a visitor visits your site, they’ll do anything at all. Furthermore, not all encounters are meaningful to FID. […]

There will be moments when the main thread is occupied for a long time, and there will be occasions when the main thread is occupied for a short time (when the main thread is completely idle).

In other words, a wide range of users will have FID values ranging from zero to quite high.

Why Do Most Sites Fail FID

This relatively new measure was not considered when many CMSs, themes, and plugins were developed.

Many publishers are shocked to learn that their sites failed the First Input Delay test because of this.

Web software developers are responding to publishing industry needs for varied code standards.

It’s not the content management system developers who blame creating products that don’t meet these standards.

WordPress, for example, fixed a flaw in the Gutenberg website editor that was lowering the editor’s score.

Gutenberg is a block-based interface for creating websites. A widgets block, a contact form block, a footer block, and so on are all present.

For example, the process of producing a web page can be seen as a series of building bricks, with different blocks being used to form a page.

There are a variety of blocks, each of which has a distinct appearance and behaviour. CSS style codes are assigned to each block, and many of these codes are exclusive to only that block.

It’s common to practise to generate a single style sheet that includes all of the styles that are specific to each block. Having a central location for all code related to blocks makes it logical to do this.

Consequently, WordPress would load all of the styles for each of the twenty blocks on a page, even if none of them was being utilized.

When CSS was packaged in this fashion, it was widely accepted as best practice.

Because of the introduction of Core Web Vitals, this method is now considered bloat.

In no way is this meant to attack the WordPress creators. Their work was spectacular.

To put it another way, this is just a demonstration of how quickly new standards may get bogged down in software development.

We went through the same situation when we transitioned to a mobile-first website design.

Improved performance in GUTENBERG 10.1.

A new feature in WordPress 10.1, Gutenberg, allows only the styles being used to be loaded, rather than the ones that aren’t.

WPMU DEV just got a significant boost, and it’s good news for everyone involved.

The time has come to address the issue of first-input delay.

We should anticipate seeing more and more CMS, theme, and plugin authors adopting First Input Delay-friendly coding methods in the future.

However, the onus is on the publisher to reduce First Input Delay in the interim. The first step is to grasp this concept.


Report on Chrome’s User Experience

Google’s page speed tool, PageSpeed Insights

Chrome’s Lighthouse development tools

Webmaster Tools at Google (Core Web Vitals report)

Improve the Delay of the First Input

The First Input Delay

Performance Metrics Focused on the User

Core Web Vitals Measuring Script on GitHub

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