Web Application Performance: 9 Ways to Speed Up Your Site

You’ve poured $70K into Instagram ads for tomorrow’s product drop. At midnight, the traffic hits, but your product pages take four seconds to become usable. Data shows that 40% of shoppers will leave before they ever see the add-to-cart button. 

Slow web application performance costs sales—whether you’re running a big campaign or not. Shoppers make decisions in milliseconds, and a sluggish site erases months of growth. Hours later, you’re left with unsold inventory and a marketing budget that’s converted only half of its forecasted return on ad spend (ROAS). 

Ahead, you’ll learn 2025 web performance tactics that cut load times, lift conversions, and protect every dollar of ad spend. 

What is web application performance? 

Web application performance refers to the real-world speed, responsiveness, and visual stability that your users experience each time they load a page or tap a button. Google captures these dimensions with three Core Web Vitals:

1. Largest Contentful Paint (LCP) for loading speed
2. Interaction to Next Paint (INP) for responsiveness
3. Cumulative Layout Shift (CLS) for visual stability 

Sites that maintain these metrics within Google’s “good” threshold can enhance usability and rankings—and prevent shoppers from bouncing. 

Why web performance matters for ecommerce

Every click on your storefront is a test of patience. If pages hesitate, shoppers don’t—they move on, leaving your inventory behind.

Web performance impacts your bottom line in three big ways:

1. Lower customer acquisition costs (CAC): When your Google Quality Score is lower, which is partially based on your landing page experience, you drive bids and CACs up. 
2. Better search rankings: Core Web Vitals are also ranking signals. If they are considered “below average,” you’ll rank lower in SERPs. 
3. Higher mobile engagement: Mobile devices now account for 62% of global web traffic. Much of that takes place over cellular networks, where higher latency (the delay between user action and website response) makes your slow pages even more frustrating for customers. A higher-performing web application loads pages fast and keeps mobile shoppers engaged.

Core Web Vitals 2025: New benchmarks

As mentioned, Google measures performance based on three metrics: INP, LCP, and CLS. As of March 2024, INP officially replaced First Input Delay (FID) as a Core Web Vital. Each metric has a different purpose:

Interaction to Next Pain (INP)

INP looks at the latency of every interaction on your page. Your slowest interaction becomes the reported score. Every tap or click should feel instantaneous; when shoppers sail through variant selectors and the checkout without hesitation, conversion rates rise.

Largest Contentful Paint (LCP)

LCP tracks how quickly the largest element becomes visible. When this main image or headline appears before a shopper considers bouncing, confidence in your page speed remains intact, and session depth grows.

Cumulative Layout Shift (CLS)

CLSquantifies unexpected page movement. Shoppers can tap the right size, color, or CTA without “page jank,” or sluggishness in your store’s user interface.

Google’s Core Web Vitals thresholds

Foundational web performance metrics

Before you diagnose Core Web Vitals, focus on these signals that reveal the root causes of slowness.

Time to first byte (TTFB)

TTFB measures how long the server takes to send the first byte back to the browser after a request. High TTFB often comes from overly complex page logic or fetching too much data before rendering. This slows the response, which drags down LCP and INP.

Speed index

Speed index tracks how quickly content above the fold (the portion of the page immediately visible in the user’s browser window) becomes visible. It maps closely to a shopper’s perceived load speed. 

Error rate and peak response time

Even a perfectly fast web page is useless if it fails. Error rate measures the share of requests that return failures (like 4xx or 5xx codes). Peak response time shows the slowest page load during traffic spikes. Both show when your site struggles—an important reminder that reliability is just as important as speed.

Tools and techniques to measure performance

Now that you know the metrics to track, it’s time to understand the tools you’ll use to monitor and act on them all. 

Use a mix of in-browser tools, observation platforms, and Shopify’s dashboards to see what shoppers experience and why.

Web performance monitoring and browser dev‑tools 

Your browser contains built-in toolsets for developers. They’re accessible in Chrome, Firefox, and Safari by right-clicking an item on the page and selecting “Inspect.” 

You can also leverage user-friendly software designed to evaluate web performance metrics, which include Google PageSpeed Insights, WebPage Test, and Pingdom.

Third‑party APM and RUM suites

Application performance monitoring (APM) services like New Relic, Dynatrace, and Datadog are paid, external software suites that monitor web performance as well as server performance, application code, and infrastructure metrics.

Combine with real user monitoring (RUM) to capture data from every shopper’s device. Together, APM uncovers server-side issues and RUM shows how they manifest in customers’ browsers. 

Shopify analytics dashboards

Inside your Shopify admin, you’ll find Web performance reports that show your store’s real Core Web Vitals data. 

Open Online Store → Themes to see the performance metric summary banner, which tracks your store’s P75 LCP, INP, and CLS scores over the last 30 days and flags them as Good, Moderate, or Poor. The charts use Google’s “good” cutoffs so you can quickly see areas that need work.

Click any metrics and jump right into Over Time reports. This tracks how theme edits, app installs, or code changes affect your metrics across any date range. 

You can also access Page Type and Page URL reports to see whether certain pages are responsible for performance changes. 

📚 Learn more about setting up custom web performance dashboards on Shopify.

Strategies to boost web application performance

1. Optimize images for faster load times
2. Minimize page requests (HTTP/2 and HTTP/3 requests)
3. Use a content delivery network (CDN)
4. Leverage serverless and edge functions
5. Implement caching
6. Optimize code
7. Implement lazy loading
8. Adopt AI-based performance monitoring

Once you’re monitoring web app performance, the next step is to optimize your performance metrics. These best practices help make your web app run more quickly and responsively to improve your customers’ shopping experience: 

1. Optimize images for faster load times

Win: Optimized images reduce page weight, speed up load times, and keep shoppers engaged.

Images can be large files, taking a long time to download and render properly for users. The good news: Shopify’s content delivery network (CDN) automatically serves images in modern image formats like WebP and AVIF, compressing them to reduce file size while maintaining image quality.

However, it’s still important to provide properly structured images in your theme. Include “width” and “height” attributes so your shopper’s browser reserves space before the image loads and avoids layout shifts. Additionally, using the srcset and sizes attributes tells the browser which versions of the image are available. The browser can then deliver the best size for the shopper’s screen resolution and network speed.

2. Minimize page requests (HTTP/2 and HTTP/3 requests)

Win: Fewer requests mean pages load faster.

HTTP (Hypertext Transfer Protocol) requests are attempts by a browser to fetch the necessary resources for rendering a web application. The more requests there are, the longer it takes to display your store. 

You can reduce these requests by: 

• Consolidating CSS and JavaScript into fewer files. HTTP/2’s multiplexing removes the need for extreme mega‑bundles, but shipping 40 tiny modules still wastes header bytes and prioritization slots.
• Each 301 or 302 forces an extra round trip even on HTTP/3. Audit your high‑traffic URLs, like your homepage, product, and cart pages, and update internal links to their canonical targets.
• Load review widgets, chat scripts, and analytics tags using async/defer attributes or dynamic imports so they don’t contend with above‑the‑fold CSS and JS on the multiplexed streams.

3. Use a content delivery network 

Win: CDNs shorten the distance between shoppers and your assets, reducing latency.

Content delivery networks are geographically distributed servers strategically located throughout the globe to deliver static assets—like images, JavaScript files, fonts, and video files—to nearby users. 

This reduces the distance data must travel, decreasing loading times. Without CDNs, users in different locations would retrieve assets from a single server, increasing loading times due to longer geographic distances.

Every Shopify store automatically benefits from a Cloudflare-powered CDN, at no extra cost. Other CDNs include Akamai and CloudFront. 

CDN vs. edge vs. serverless

4. Leverage serverless and edge functions

Win: Running code closer to shoppers cuts response times and keeps performance steady during traffic spikes.

In broader ecommerce, serverless platforms or edge functions, like Shopify Functions or AWS Lambda@Edge, allow logic—such as pricing, currency exchange, and inventory checks—to run without maintaining dedicated servers. Because the code scales automatically and, in the case of edge runtimes, executes near the shopper, response times drop, and you don’t pay for idle servers. 

Shopify is already embracing this approach with Shopify Functions, a serverless framework that lets developers customize parts of Shopify’s platform (such as discounts or checkout) on a fast, managed infrastructure. While you don’t have to configure servers yourself, it’s helpful to understand why serverless and edge execution are becoming the industry standard: they lower your TTFB and keep INP inside Google’s “good” zone during traffic spikes. 

5. Implement caching

Win: Caching makes repeat visits and page reloads feel almost instantaneous.

Caching is the practice of storing copies of frequently accessed or difficult-to-compute data in the user’s browser so the resources don’t need to be downloaded every time the user visits your site. 

Start by identifying the content you want to cache (normally images, CSS files, or JavaScript files) then enable cache-control headers on your web server, which tell the browser how long to store the given resources.

Shopify already manages caching for you through both its theme renderer and its built-in CDN. Your store automatically benefits from fast repeat loads—you don’t need to configure anything.

6. Optimize code

Win: Cleaner, smaller code speeds up page loads and improves performance metrics.

Minifying code is the process of reducing the size of a web app’s source code while preserving its functionality. To do this, remove unnecessary characters, white spaces, comments, and line breaks from your code. Tools like UglifyJS (for JavaScript), CSSNano (for CSS), and HTML-Minifier (for HTML) can automate this process for you or your programming team.

On Shopify, your static text-based assets are already minified automatically through our CDN. That means your storefront benefits from leaner code without any extra steps.

7. Implement lazy loading

Win: Lazy loading reduces page weight up front, so shoppers see critical content faster.

Lazy loading is a software design technique that loads images, videos, and other noncritical resources only when they’re needed—such as when the shopper scrolls down to see them—rather than loading everything upfront.

On Shopify, you can implement this by adding the loading="lazy" attribute to images below the fold. However, if you apply lazy loading to above-the-fold content, like your hero image, it can actually delay when your page looks usable and hurt your LCP score.

You can also use the Intersection Observer API, which is a built-in JavaScript tool to detect when an element enters the viewport and load it dynamically. You can also enable scroll-event listeners or use lazy-loading libraries such as LazyLoad or Lozad.js.

8. Adopt AI‑based performance monitoring

Win: AI tools can help spot performance issues, helping teams fix problems faster.

AI-powered APM leverages machine learning capabilities to uncover performance issues and often self-correct them before customers notice any difference. The platform ingests logs, traces, and key metrics, then:

• Isolates the root cause by cross-referencing spikes in response time with code commits and infrastructure events
• Forecasts potential issues using trend analysis, so you get more time to scale or patch
• Auto-tunes settings like cache size and thread pools in real time to keep Core Web Vitals green (If you’re on Shopify this isn’t relevant.)

For example, Datadog Watchdog runs unsupervised ML on your logs and RUM data to auto-detect latency spikes or error surges. It could flag a sudden INP increase on your product pages in seconds, so you could roll back a bad deploy. 

Continuous monitoring and regression prevention

Your store’s web application performance isn’t a one-time fix. Theme edits, app installs, and code changes can all affect Core Web Vitals, so continuous monitoring is essential to catch regressions before they impact conversions.

Shopify’s built-in web performance reports track your LCP, INP, and CLS over time and flag whether scores are good, moderate, or poor. You can also compare results across page types or specific URLs to quickly see where your store is slipping and take action.

By monitoring consistently, you protect site speed and keep shoppers moving from product page to purchase.