Have you ever clicked a button on a website and had to wait what felt like an eternity for something to happen? That frustrating delay is a symptom of poor First Input Delay, or FID. FID measures the time between when a user first interacts with your site (e.g., clicks a link or taps on a button) and the moment when the browser is actually able to respond to that interaction.
A sluggish FID can single-handedly ruin an otherwise great user experience. In fact, Google has made FID a core ranking factor in their search algorithm as part of their Page Experience signals. So poor FID doesn't just annoy your users, it can actually hurt your search rankings too.
But don't fret! While FID issues can cripple your site's usability and searchability, there are proven ways to optimize and improve your FID scores. In this guide, we'll dive deep into the world of FID - what exactly it measures, why it matters so much, how to accurately gauge it, and most importantly, developer-approved strategies to nip those pesky delays in the bud.
So grab a coffee, settle in, and get ready to become an FID master. Your users (and your search rankings) will thank you.
Defining First Input Delay: A Primer
Let's start by making sure we're on the same page about what FID is and what it measures.
In simple terms, FID is the delay between when a user first tries to interact with a page to the moment when the browser can actually respond to and process that interaction. It essentially measures how quickly your site responds to user input once the page has loaded.
An interaction can be things like:
- Clicking a button or link
- Checking a checkbox
- Selecting from a dropdown menu
- Typing into a search field or text box
The key point is that FID measures the first interaction after page load. So, it reflects how soon a user can actually start engaging and accomplishing what they came to your site to do.
Imagine you're a user. You go to a site eager to read an article or purchase a product. The page comes up reasonably fast, you see what you want, so you click it...and nothing. The page sits there, stubbornly ignoring your request. As the milliseconds tick by, your frustration grows. You may try clicking again or give up entirely and try your luck elsewhere. That dead time between your intent and the site's response? That's poor FID in action.
Why First Input Delay Matters (Spoiler: A Lot!)
So why should you care about FID? Well, like most web vital metrics, it all comes down to user experience and how it impacts your business goals.
FID and User Experience
A high FID (meaning a long delay) directly equates to a poor user experience. On modern websites, users expect near-instant feedback on their actions. Even a delay of a few hundred milliseconds can be noticeable and start to degrade the experience.
Consider some of the negative impacts a high FID can have:
- Frustration and annoyance as users wait for their actions to take effect
- Confusion about whether their click/tap worked, often leading to erroneous duplicate attempts
- Abandonment if the delay is long enough to make users give up and try another site
- Mistrust in your site's quality, reliability, and credibility
On the flip side, sites with fast FID responses feel slick, responsive and high-quality to use. When every interaction feels seamless and snappy, users stay engaged, complete their tasks, and leave with a positive impression.
FID and SEO
While FID is most tangibly felt by your end users, it can also have a big impact on your search rankings behind the scenes. Google has stated that FID is a core search signal used in its ranking algorithms.
Sites that provide a fast, responsive experience, as measured by FID, are more likely to rank higher in search results. Conversely, a poor FID can drag down your rankings and make it harder for users to find your site organically.
Google's reasoning is clear—they want to serve up the highest-quality sites that provide the best experience to searchers. A responsive site, as measured by FID, is a key part of that equation.
Measuring and Quantifying First Input Delay
Now that we know what FID is and why it's so critical, let's talk about how to actually measure it. Accurately quantifying FID is the first step to identifying issues and improving your scores.
There are a few key ways to measure FID:
-
Chrome User Experience Report (CrUX): This is a public dataset of real-world, anonymized user experience data. You can query your site's FID data from CrUX via tools like PageSpeed Insights or the CrUX API.
-
Search Console: Google Search Console now includes a Core Web Vitals report that shows your site's FID data (among other metrics) over time.
-
JavaScript: You can track FID in your own site's code using the PerformanceObserver API in JavaScript. Here's a sample code snippet:
new PerformanceObserver((entryList) => {
for (const entry of entryList.getEntries()) {
const delay = entry.processingStart - entry.startTime;
console.log('FID candidate:', delay, entry);
}
}).observe({type: 'first-input', buffered: true});
- Real User Monitoring (RUM) Tools: Many third-party RUM tools, like Raygun Pulse or New Relic Browser, track FID out of the box. These can provide additional context and help tie FID to larger user journeys and business metrics.
Whatever method(s) you use, the key is to consistently track your FID scores over time. This will let you spot issues, measure the impact of optimizations, and ensure that you're continually providing a responsive experience.
Strategies for Optimizing First Input Delay
You've measured your FID and identified some room for improvement. Great! Now what? Let's dive into some proven strategies and code samples you can use to optimize your FID scores.
Minimize Main Thread Work
One of the leading causes of input delays is long tasks monopolizing the browser's main thread. The main thread is where the browser processes user events, so if it's tied up with other work, it can't respond promptly to user interactions.
To minimize main thread work:
- Break up long JavaScript tasks into smaller, asynchronous ones. Avoid any tasks over 50ms long.
- Use a web worker for costly operations like complex data processing. This offloads the work from the main thread.
- Defer non-critical JavaScript that doesn't impact above-the-fold content or functionality until after interaction.
Here's an example of code splitting and deferred loading a non-critical script:
const myHeavyLibrary = await import('./path/to/heavy-library.js');
// Only load on user interaction like button click
document.querySelector('#my-button').addEventListener('click', () => {
myHeavyLibrary.init();
});
In addition to reducing main thread work, you can also optimize your JavaScript more broadly:
- Minify and compress your scripts to reduce their parse/compile time
- Remove any unused or unnecessary code
- Lazy load scripts that aren't needed immediately or only run below the fold
- Employ code splitting to break up large bundles
Reduce Reliance on Third-Party Code
Third-party scripts for ads, analytics, social widgets, etc. can be a major drag on FID. You're at the mercy of how performant and party's code is. To mitigate this:
- Audit your third-party scripts and remove any that aren't essential
- For the ones you do keep, see if there are more lightweight alternatives
- Load third-party scripts asynchronously or defer them so they don't block the main thread
- Set performance budgets for third parties and hold them accountable
Here's an example of asynchronously loading a script:
<script async src="https://example.com/script.js"></script>
Optimize Your Server
Your server's response times are a key factor in FID. Slow server responses mean the browser waits instead of responding to user input. Some tips:
- Utilize caching and CDNs to reduce full-page loads
- Optimize database queries that run on user interactions
- Compress resources to minimize data transfer and speed up fetches
- Implement HTTP/2 or even HTTP/3 for more efficient data transfer
Avoid Long-Running CSS
While CSS is less of an FID factor than JavaScript, a long-running CSS task can still block the main thread. Optimize your CSS by:
- Minifying to reduce size and parse time
- Removing any unused styles
- Using efficient selectors that are quick to match
Tools of the FID Trade
In addition to manual code optimizations, some great tools can help you measure, debug, and monitor FID:
- Chrome DevTools Performance Panel: Provides detailed flame charts of main thread activity to identify long tasks
- Lighthouse: Automated tool for auditing web performance, including FID
- WebPageTest: Allows for detailed performance testing from multiple locations/devices
- PageSpeed Insights: Analyzes a URL and suggests performance optimizations, including for FID
These tools can provide valuable data and insights to guide your FID optimization work.
Putting FID Optimization into Practice
Theory and guidance are great, but let's look at real-world examples of FID optimization.
Tokopedia, one of the largest e-commerce sites in Indonesia, implemented various web performance optimizations, including reducing render time, optimizing JavaScript, and leveraging a multi-cloud architecture. Through these efforts, Tokopedia significantly improved site speed, achieving a 35% increase in click-through rates and an 8% lift in conversions.
- Reducing render time from 14 seconds to 2 seconds on 3G connections
- 35% increase in click-through rates
- 8% increase in conversions
- Migrating to a multi-cloud architecture on AWS
https://cloud.google.com/customers/tokopedia
Optimize Your Server
Your server's response times are a key factor in FID. Slow server responses mean the browser waits instead of responding to user input. Some tips:
- Utilize caching and CDNs to reduce full-page loads
- Optimize database queries that run on user interactions
- Compress resources to minimize data transfer and speed up fetches
- Implement HTTP/2 or even HTTP/3 for more efficient data transfer
Avoid Long-Running CSS
While CSS is less of an FID factor than JavaScript, a long-running CSS task can still block the main thread. Optimize your CSS by:
- Minifying to reduce size and parse time
- Removing any unused styles
- Using efficient selectors that are quick to match
Tools of the FID Trade
In addition to manual code optimizations, some great tools can help you measure, debug, and monitor FID:
- Chrome DevTools Performance Panel: Provides detailed flame charts of main thread activity to identify long tasks
- Lighthouse: Automated tool for auditing web performance, including FID
- WebPageTest: Allows for detailed performance testing from multiple locations/devices
- PageSpeed Insights: Analyzes a URL and suggests performance optimizations, including for FID
These tools can provide valuable data and insights to guide your FID optimization work.
Putting FID Optimization into Practice
Theory and guidance are great, but let's look at a couple of real-world examples of FID optimization in action.
The Future of FID
As with all things web performance, FID standards and expectations will continue to evolve. As our devices, networks and user preferences advance, so too will our ability to provide faster, more seamless interactions.
Emerging technologies like 5G and edge computing promise to reduce data transfer times and processing latency. As more logic and rendering shifts toward the user's device, we may see a reduction in main thread pressure and a resulting drop in FID issues.
However, these same advancements also raise user expectations. What qualifies as "fast enough" will likely get even more stringent as users become accustomed to near-instant speeds. Staying on top of FID optimization will be an ongoing process.
Additionally, as Google and other search engines continually refine their algorithms, expect FID to maintain or even increase in importance as a search ranking signal. Monitoring and optimizing for FID is crucial for maintaining competitive search visibility.
Wrapping Up: Your FID Mastery
We covered a lot of ground in this deep dive on First Input Delay. To recap, FID is a crucial metric for measuring how quickly your site responds to user interactions. It's a key part of overall user experience and a significant factor in search rankings.
By tracking your FID scores, identifying problem areas, and implementing smart optimizations like code splitting, removing long tasks, and improving server response, you can provide snappy interactions that delight users and impress search engines.
Remember, every millisecond counts when it comes to FID. Users are increasingly demanding, and even small delays can have outsized impacts on their experience and your bottom line. But by following the strategies and best practices we outlined, you're well equipped to be an FID master.
So what are you waiting for? It's time to put your newfound FID skills to the test. Audit your site, set some goals, and start optimizing. Your users (and your search rankings) will thank you.
And if you need some help along the way, the team at ContentBasis is always here to lend a hand. Our performance experts can guide you through the ins and outs of FID optimization to ensure your site is providing a top-notch, delay-free experience. Just drop us a line.
Happy FID optimizing!
Frequently Asked Questions (FAQs)
-
What is a good FID score?
- According to Google, sites should strive to have an FID score of 100 milliseconds or less. A score between 100 and 300 ms needs improvement, and anything over 300 ms is considered poor.
-
How does FID relate to other web performance metrics?
- FID is part of Google's Core Web Vitals, along with Largest Contentful Paint (LCP) and Cumulative Layout Shift (CLS). Together, these metrics provide a comprehensive view of a page's loading, interactivity, and visual stability.
-
Does FID affect ranking in search engines other than Google?
- While Google has been the most vocal about using FID as a ranking factor, other search engines like Bing and DuckDuckGo also factor page experience into their algorithms. Optimizing FID is likely to have positive impacts across all search engines.
-
What causes high FID scores?
- The main causes of high FID are long tasks monopolizing the main thread, unoptimized JavaScript, slow server response times, and render-blocking or long-running CSS and third-party scripts.
-
Can you improve FID without code changes?
- Many FID optimizations require code changes like splitting bundles, deferring scripts, etc. However, some improvements can be made through server and caching configurations. Still, the biggest FID gains typically come from front-end code optimizations.
