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Client-Side Performance Testing: Metrics to Consider

September 9, 2021
Prathitha IyengarPrathitha Iyengar
Prathitha Iyengar

You can conduct performance testing to ensure that the software is working properly. Software performance testing is divided into two distinct categories. 

  • Client-side Testing: The scope of client-side testing is to evaluate end-to-end scenarios while evaluating the rendering of elements such as CSS and JavaScript files. 
  • Server-side Testing: The scope of server-side testing is to evaluate logical scenarios, focus on the application behavior under user load, and check the server response time. 

In both of these testings, experiments are run to check performance of the website. These tests check the application for bottlenecks, review the time it takes to load under different speeds, and analyze its loading speed, stability, and scalability. 

In the instance of conducting client-side performance testing, what we are checking is: 

  • How fast and efficient the application is. 
  • The response time of a web application if the user is using the website for the first time and when they revisit the website the second time. 
  • The time it takes to render web page elements to the users. 
  • The time it takes for the user to interact with the first web element and the average time to display the web content.
Recommended Post: Your Mobile Performance Testing Questions Answered

The Objective of Client-Side Performance Testing 

The objective of client-side performance testing, or any performance testing, is to ascertain, evaluate, and make necessary changes in the problem areas.

Check out: Best Practices for Application Performance Testing

For optimal results on your client-side performance testing, you can: 

  • Compress the images and the JS (JavaScript) code. 
  • Provide faster response times, enable better cache techniques. JS code caching reduces the start-up time of websites. 
  • Ensure implementation of necessary changes after evaluating the results of server-side performance testing. 
  • Minimize HTML, CSS (Cascading Style Sheets), and JavaScript content. 
  • Remove all unused CSS and JavaScript codes. 
  • Upgrade the server hardware to create more memory space, if needed. 

To study, analyze, and make necessary changes in the application, software engineers use metrics to study the key performance indicators to form a conclusion.

Also check: Performance and Load Testing for Mobile Applications

Metric Performance Testing 

Metrics define the performance of an application by estimating the health, quality, and productivity of the software. A metric establishes the quality of the performance in quantitative terms. Studying metrics can help software engineers and web developers in the following areas: 

  • It assists in understanding how much improvement is required and where it is required. 
  • It helps with the early detection of problems within an application or website. 
  • It is a determiner to check the progress of the development. 
  • They provide critical insights about application/ software behavior. 
  • It is a measure of quality assurance and is easy to discuss and improve upon due to its quantitative nature. 
  • It also helps developers make important decisions, such as estimating the cost of a project and scheduling a future project. 
  • It evaluates whether the current technology needs any modifications.
Read: Performance Testing - An Ideal Process for Successful Applications

Types of Software Testing Metrics

  • Process Metrics: This metric defines the characteristics and execution and is essential for improving the software development life cycle. 
  • Product Metrics: It defines a product’s performance, design, quality, and complexity to tackle its quality. 
  • Project Metrics: It measures the overall quality of a project. It calculates the team's performance, calculates the project’s costs and defects, and estimates the deliverables.
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Client-side Metrics in Performance Testing 

Client-side metrics in performance testing test the application's response for different clients using different platforms such as desktop, mobile, smart TV, etc. Client-side metrics check interaction speed, location, and connection speed. 

Also read: Important Uses of Mobile App Performance Testing Tools

Important Client-side Metrics in Performance Testing 

  • Time to First Byte (TTFB)
    Time to First Byte is a client-side metric that measures the time spent connecting with the server and downloading the site's contents. The acceptable range of TTFB is between 100-500ms (milliseconds), with anything being under 100ms is even better.
    The unacceptable range of TTFB is anything more than 500ms. Developers can improve upon this by reducing HTTP requests, optimize the application code and database queries, and use a content delivery network.
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  • CPU Idle Time
    CPU Idle Time metric measures the amount of time the CPU was not busy and was waiting for a response from the third party.
  • Payload
    In web development, the word 'payload' refers to the difference between essential information in a chunk of data and the information used to support it. In the context of malware, 'payload' refers to the transmission of malicious code via worms, phishing emails, and other mechanisms.
  • Time to Interact
    Time to Interact or TTI metric measures the time it takes for a website to become fully interactive. A fully interactive page displays useful content and is responsive to user interaction within 50 milliseconds. The acceptable range of the TTI metric is between 0 and 7.3 milliseconds. Between 0-4 milliseconds, it is fast, and between 4.1-7.3 milliseconds is moderate.
    The unacceptable range of the TTI metric is anything above 7.3 milliseconds which is considered slow. Some ways to improve the TTI score are reducing payloads with code splitting, decreasing JavaScript, lowering main thread work, and optimizing third-party JavaScript.
Check out: A Guide on How to Use HS Tunnel
  • Speed Index
    The Speed Index metric calculates the time it takes for the contents of a page to become visibly populated. They are measured in milliseconds, and the lower the score, the faster is the loading performance.
  • Load Time
    The Load time metric measures the time it takes for a page to appear on your screen. It is calculated from the time you click on a link to when it finishes loading to completion. It is crucial because it determines search engine ranking and increases customer satisfaction.
    You can reduce the load time by minimizing the file size, combining HTML, CSS, and JavaScript files, choosing the most appropriate hosting option, and enabling browser caching.
    The acceptable range of load time is a contentious subject, with users wanting the optimal time to be 3 seconds, while the average load time is 15 seconds.
  • Time to Render
    This metric calculates its time to process and display elements to the users.
See: Challenges in Performance Testing on Mobile Devices


Customer satisfaction is vital when it comes to your website. Performance testing is useful for checking the usability of your website. Client-side metrics in performance testing are tools that help you in this context.


Q1. What is client-side profiling?

A1. Client-side performance tests help verify if an application is fast and efficient enough. It involves considering a single user's point of view and checking a web application's response time.

Q2. What are some examples of performance metrics?

A2. Some examples of performance metrics are productivity, profit margin, scope, and cost. A business can track these metrics to determine if the team meets target objectives and goals. Each area of a business will have its key performance metrics.

Q3. When to use client-side and server-side testing?

A3. You can run client-side A/B testing when you deploy an internal team of marketers to run experiments without needing to change the code. You can run server-side a/b testing when the scope of an experiment is more extensive, for example, when you need to make changes at the product level.

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Client-Side Performance Testing: Metrics to Consider

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