Exploring Performance Testing Approaches: Isolated Endpoint, Endpoint Flow and UI Performance

Dive into this simple guide on performance testing for software applications! We're exploring three different testing methods - isolated endpoint, endpoint flow, and UI performance. With clear examples of their pros and cons, this article will help you choose the right method for your needs.

Author: Vlad Ivascu

Performance testing plays a crucial role in ensuring the reliability and efficiency of software applications. To effectively test the performance of the application, different approaches may be used. In this article, we look at three ways of doing performance testing: isolated endpoint, endpoint flow, and UI performance. We will explore the advantages and limitations of each approach, helping you determine the most suitable strategy for your testing needs.

Isolated endpoint – one endpoint

In performance testing, you can either call a single URL or multiple URLs in succession. The simplest method is to test individual API endpoints exclusively. Unlike a user opening a browser and filling out forms, a single API performance test only focuses on the underlying server request. This approach is particularly useful in complex applications that involve multiple components and would require substantial effort to replicate in a testing environment. You can test only the required functionality using one endpoint call, making it the most cost-efficient approach.


  • direct approach
  • simple writing of a single call test - easier to set up and execute tests for a single endpoint, as opposed to designing tests for an entire system
  • useful in more complicated applications that involve several components and would require a lot more effort to reproduce in a test environment.
  • cost-efficient
  • isolation of issues - if there's a performance problem, it's easier to identify and isolate when testing a single endpoint. This can speed up the debugging and problem-solving process.


  • not always a real-life scenario
  • does not simulate real users interacting with page elements
  • lack of context - while testing a single endpoint can provide detailed results, it may not reflect the system's overall performance. Real-world users interact with multiple components, not just a single endpoint.
  • oversights - since the focus is on one endpoint, you might miss issues that only occur when multiple endpoints or services interact.

Endpoint Flow

If you need to run performance tests towards multiple endpoints, there is an approach that could simplify your API testing strategy. The advantage of this technique would be that it saves time in development and execution of tests, as you can extend your functional tests into functional performance tests. Also, the API functional performance testing allows you to evaluate not only whether the API can handle a specific performance pattern but also how well it handles it.

Usual performance tests reveal whether the API fails or not in response to a particular context (based on KPIs) while with functional performance testing, you can track the functionality under different performance conditions. For this approach, a good practice would be to start with the most used flows from your application. This can be done by having analytics tools or platforms to gather data on user interactions with your application. Also, you should add wait times between calls because in real life the user doesn’t go from one action to another instantly.


  • easy to extend functional tests into functional performance tests
  • easy to see if the API can handle a given performance pattern
  • uncover performance issues that may arise due to the interaction or dependencies between different endpoints or services
  • closer to a real-life scenario - testing a flow of endpoints is more reflective of real-world user interaction with the application. It helps to understand the application's behavior under conditions that closely mirror actual usage.
  • identify bottlenecks - by testing the interaction between multiple endpoints, you can identify performance bottlenecks that may not be apparent when testing single endpoints in isolation
  • end-to-end performance - it gives a holistic view of the system's performance and reliability, considering the entire workflow instead of just individual parts.


  • more complexity in writing the performance test
  • more analyze needed to identify the realistic user flows
  • if a performance issue is found, it may be harder to pinpoint the exact cause because it could be due to any of the multiple endpoints or their interaction.
  • can consume more resources and take longer to execute compared to testing a single isolated endpoint.
  • maintaining the test setup to reflect changes in the flow can be challenging as the application evolves
  • if one endpoint in the flow is not working correctly, it may prevent testing of subsequent endpoints in the flow
  • not simulate real users interacting with page elements

UI Performance

Since performance API testing doesn't give you feedback on how long your pictures took to render on your user's browser or how quickly pages render in different browsers, UI performance testing should be part of each project. API performance testing does not simulate real users interacting with elements and doesn't run client-side scripts. Before doing UI performance tests, you must define the expected load times for a webpage or the desired frames per second for animations.

For UI testing, you only explained what UI testing is, not how it is achieved, which you did for the other two strategies. It might be worth adding something on how UI testing is actually implemented like you did for endpoint flow testing.

As an example, by using a tool like Lighthouse from Chrome DevTools, you can analyze specific metrics like the time taken for the first piece of content to appear on the screen, how quickly content is visually displayed during page load, or the total time taken for the page to become fully interactive. Using Lighthouse for UI performance can help you with recommendations that include delaying the loading of non-essential CSS/JS, optimizing images, or making better use of browser cache.


  • the primary advantage of UI performance testing is that it helps ensure a good user experience. If the UI is slow or unresponsive, it can frustrate users and lead them to abandon the application.
  • gives feedback on how long the pages(pictures/elements) take to load
  • can help with having an improved SEO ranking - search engines consider page load times as a ranking factor. Faster-loading pages can positively impact your website's search engine rankings, leading to increased visibility and traffic.


  • limited coverage because it primarily focuses on the front-end user experience – does not detect issues related to back-end performance or server-side problems that could impact the overall user experience, doesn't give feedback on API response times
  • the UI may behave differently across various devices, screen sizes, and browsers so testing across a wide range of configurations can be time-consuming and may require additional tools and expertise.


Performance testing is important to ensure that applications can handle expected workloads and offer a positive user experience. Selecting the right approach depends on the specific needs and context of the application being tested.

  • Isolated Endpoint testing is best for focused analysis but may miss bigger-picture issues,
  • Endpoint Flow testing provides a complete system view but can be more complex and resource-consuming.
  • UI Performance testing ensures a positive user experience but can be time-consuming

Understanding these pros and cons helps you make informed decisions and choose the testing approach that best aligns with your goals and the nature of the application, ultimately leading to more efficient and effective performance testing.