Top 8 Web Application Performance Metrics

Top 8 Web Application Performance Metrics

Table of Contents


Web application performance metrics help determine certain aspects that impact the performance of an application. 


This article discusses eight key metrics, including:


  • User Satisfaction—also known as Apdex Scores, uses a mathematical formula in order to determine user satisfaction. 
  • Time to First Byte—measures the time it takes to render the application on end-user devices. 
  • Time to First Paint—measures how long it takes for the initial pixels to show on the screen.
  • Speed index—checks how readily the above-the-fold content appears on a screen.
  • Time to interact—measures how much time passes before a web page is fully interactive.
  • DNS lookup time—measures the time it takes for a domain lookup to occur while the browser loads the page.
  • Error rate—tracks the percentage of request issues you incur in relation to the overall number of requests.
  • Peak response time—measures the longest response time for a total number of requests that travel across the server. 


Web performance is rapidly evolving, with new trends like Google’s Core Web Vitals (CWV), increasing use of images and video on web pages, and the rollout of 5G. We’ll present three methods that can help you adapt to these changes and boost the performance of your web applications.


Key Takeaways

  1. Combine and shrink files to reduce their number and size. Minification removes unnecessary characters, speeding up load times.
  2. Store static or infrequently changing resources in caches for faster access. Choose private or shared caches and consider CDNs.
  3. Execute instructions in advance, enhancing performance. Use DNS, link, or prerendering prefetching based on user behavior analysis.


8 Key Web App Performance Metrics

User Satisfaction / Apdex Scores

The application performance index, known as the Apdex score, is now an industry standard for tracking an application’s relative performance. It functions by stating a goal for how long a specific application transaction or reb request must take. Those transactions are then labeled as failed, too slow, tolerating (sluggish), or satisfied (fast) requests. A mathematical formula is then applied to give a score from 0 to 1.  


Your selected application performance monitoring (APM) solution must automatically track satisfaction scores for each one of your web and application requests. Offering scores in a larger range, such as 0-100, rather than 0-1, is also better, as it means that insights are easier to interpret and act upon. 


Time to First Byte

TTFB is the time required to request information from the server and to transfer the information that was requested. In simple terms, it is the time from the point where you navigate to a webpage through to when it starts to render. This period of time includes:  


  • The server request can differ according to internet connection and location
  • The time needed to process a request or form a response
  • The time needed to send information based on the question


Return time equals 40% of the total TTFB. The slower the TTFB, the more time it will take for your user to view any content on your site.


Time to First Paint

“First paint”, “first contentful paint”, and “first meaningful” are all user-centric perceived performance metrics, or put another way, metrics pointing to the actual experience of the web application user. 


First paint refers to how long it takes for the initial pixels to show on the screen and tell the visitor that the content will soon load. The first contentful point indicates how much time passes before content is defined in the DOM, as text or an image, is rendered. The first meaningful point out when all the website content is loaded and ready to offer the user meaningful information. 


Speed Index

The speed index is another metric that relates to the user experience—specifically, to when and what the visitor sees. The speed index is an indicator of how readily the above-the-fold content appears on a screen. It is sensitive to the quality of the web connection and the size of the viewpoint. This makes it an essential part of optimizing web applications for different screen sizes. 


Time to Interactive

This indicator measures how much time elapses before a page is fully interactive, meaning the first contentful point takes place, event handlers are registered for most of the visible elements, and the website reacts to user action.


DNS Lookup Time

The time it takes for a domain lookup to occur while the browser loads the page. DNS lookups can add a great amount of load time to your browser, particularly if your application loads many third-party scripts.  


Error Rate

A performance metric that tracks the percentage of request issues you incur in relation to the overall number of requests. You should watch this number as any spike will indicate that you are looking at a significant failure in the near future. 


Peak Response Time

Measure the longest response time for the total number of requests traveling through the server. This will provide you with an understanding of where your web application is underperforming or having trouble fulfilling requests. It can also help you isolate the cause more easily. 



How to Improve the Performance of Your Web Application

There are a number of ways to ensure your web application performs properly.


Bundle and Minify Your Files

Reducing the overall number of files you have and optimizing these files are key parts of optimization. Minify and bundle your files to better your web application’s performance. Bundling involves combining your files to minimize the overall number. Minification involves reducing the size of individual files. 


A typical minification technique includes removing unnecessary characters that don’t have to load from CSS, HTML, and JavaScript. Some of these characters are white space characters, comments, new line characters, and block delimiters. Minification decreases the amount of code required to be requested from the server, so it may speed up your load time. 


Use Network Caching

An additional technique that is commonly used to improve the throughput and latency of an application is caching. A cache is a temporary data storage where information that has previously been fetched can be persisted for quicker access further down the track. 


The most suitable candidates for caching are those that change infrequently or static resources, including JavaScript (JS) files, pictures, and Cascading Style Sheets (CSS) stylesheets. You can also cache operations that are expensive to calculate. 


Between the client and server, a number of caches are obtainable, from browser and application caches through to content delivery networks (CDNs) and reverse proxies in front of an application server. Caches may be divided into two groups according to a proper access level—private (available only to single users) and shared (available to multiple users).


Apply Prefetching Techniques

Prefetching involves reading and executing instructions prior to user initiation. This technique is fairly common and is effective if you can anticipate user actions and, for example, load some links or content in advance. Generally, modern browsers permit prefetching by default as they make assumptions regarding user behavior patterns. UX engineers and specialists are likely to have insight into user behavior and create “hints” for browsers to do prefetching work. 


There are three main types of prefetching:


  • DNS-prefetching—this involves resolving domains into IP addresses in advance.
  • Link prefetching—if you are certain that a user will use a specific link to navigate to a certain page, you can make use of this sort of prefetching. This method is helpful for stable user journey actions, such as going to the shopping cart page once items have been added. 
  • Prerendering—this involves rendering a whole page (or certain elements) in advance.  


Prefetching is effective, but it does demand user behavior analysis to form accurate assumptions. 



In this article, I covered eight key web application performance metrics and several methods you can use to improve the performance of your application, including bundling and minifying files, using network caching, and applying prefetching techniques.


I hope this will be of help as you gain a better understanding of leveraging web application metrics to improve the performance of your applications.

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