API Load Testing Tutorial: Beginner’s Guide

What is API Load Testing?

API load testing involves evaluating the performance and scalability of an Application Programming Interface (API) when subjected to simulated heavy loads. During load testing, your testing endeavors may involve more extensive API load testing. This involves exposing your APIs to heightened request levels, prolonged durations, and a wider testing scope, spanning from individual components to complete end-to-end workflows. The objective is to verify that the API can effectively manage anticipated traffic, delivering consistent and reliable performance to your users.

API load testing may provide metrics such as response times, latency, throughput, and general API conditions to validate the performance of your website or application under the anticipated load. API load testing can be conducted in a variety of ways and there are several different types of API load tests, depending on the specific goals and objectives of your testing process.

Types of API Load Tests


  • Stress Testing: API stress tests determine the breaking point of an API by gradually increasing the load until the API fails or becomes unavailable. This helps to identify the maximum capacity of the API and any potential bottlenecks or vulnerabilities.

  • Soak Testing: API Soak tests determine the stability and reliability of an API over an extended period. You subject your API to high request rates for an extended period to detect issues that may not be visible during shorter periods of high load.

  • Spike Testing: API Spike tests determine how an API responds to sudden, unexpected spikes in traffic. This helps you identify any issues with the API’s ability to handle sudden increases in load and ensure it recovers quickly.

  • Performance Testing: API Performance tests focus on measuring the performance and efficiency of an API under different load conditions. When you’re performing performance tests, you’re measuring response time, throughput, and resource utilization.

Benefit of API Load Testing and Why You Should Do It

APIs are the backbone and fountain of most modern software solutions today, so why not load them? Load Testing APIs are crucial for assessing performance, scalability, and reliability under varying levels of concurrent usage. Avoiding downtime and bottlenecks are important to ensure that your software is working as intended and by load testing your APIs, it helps identify bottlenecks, assess resource utilization, and ensures that the API meets quality standards and service level agreements. By simulating realistic load scenarios, your organization can optimize infrastructure, plan for capacity, and deliver a consistent and reliable user experience, ultimately improving the overall performance and efficiency of your APIs.

Some of the benefits for API load testing are:

Minimize API Failure Costs

Identifying API performance issues in the initial stages, particularly before deployment, incurs significantly lower costs for an organization compared to addressing API downtime during production. The primary risk to site uptime is API downtime and this typically occurs when your APIs are unable to execute their intended functions. Conducting API load testing helps to find and fix code bugs that can result in suboptimal performance under anticipated or unforeseen stress, minimizing the cost of failure. It also makes it possible to spot implementation flaws and code oddities that might have been difficult to find which in turn, reduces API latency and improves performance.

Minimize and Mitigate API Downtime

API load testing provides insight into the API’s capacity to handle user requests without experiencing crashes, effectively preventing API downtime. It also diminishes the likelihood of API downtime by identifying and isolating requests that require performance enhancements. With load testing, your dedicated resources can be allocated to manage the heightened traffic, minimizing any occurrence of API downtime.

Enhance Your API Infrastructure

API load testing plays a crucial role in determining the appropriate infrastructure by assessing the volume of API requests and traffic across different use cases. API load testing helps to identify the maximum number of concurrent user requests a single API endpoint can handle. And with this knowledge, your teams can properly address expected traffic surges ensuring that your API infrastructure can cope with varying demands. Load testing will aid in gauging and optimizing the scalability of the API infrastructure.

Improve API Performance and Customer Satisfaction

Your API development can be difficult to implement with so many API endpoints and high user expectations. Your APIs could face performance problems such as delayed response times, latency, and throughput. By load testing your APIs, you can detect performance bottlenecks faster and enhance their performance before deploying to production for real users. Investing in improving your API’s performance is an investment in customer satisfaction which will result in customer retention and users will want to continue using your website or application.

How to Load Test APIs

1. Identify Test Objectives

Before you load testing APIs, you’ll want to consider why you want to load test the API. Some questions that you may want to ask when designing your API tests:

      • Who is your end user or target audience?
      • What flows or components do you want to test?
      • What is the user trying to achieve with your API?
      • How critical is the API to your users?
      • What happens if the API is unavailable or unreliable?
      • How will you run the test?

By answering some of these questions, you can set and define the scope of the API load tests and determine the success performance criteria you are looking for. After you have defined your API load tests, you’ll want to use the following steps to start API load testing.

2. Define User Workflow, Test Data, and More

Script your test by defining your user workflow which is the flow that your user will take/do with using your API. During this step, you’ll want to set your test data parameters and determine what data is required to run your simulated users through the API call. You’ll also want to define the URL before you load test APIs.

3. Select Load Testing Tool

Choosing an appropriate load testing tool that aligns with your testing objectives is crucial. Some popular open-source load testing tools are Apache JMeter, Gatling, and Locust. Even though these are some open-source and freely available tools, they might not provide the best features available in the market. LoadView on the other hand, offers an intuitive load testing tool that helps streamline your load testing efforts with tons of features to assist you in simulating multiple concurrent users while providing a comprehensive look into the performance metrics of your API.

4. Configuring Test Case and Scenario

Develop your test cases based on your identified scenarios. During this step, you will want to specify the number of virtual users, the type of requests, the frequency to simulate realistic usage patterns, where your virtual users are from, and many more. You may also want to decide how to simulate the traffic to test your API. You can typically do this with a load testing tool to ensure that your testing needs are met.

Depending on the requirements of your API testing, the LoadView platform allows you to choose from multiple load curves. You can define your API load tests to simulate traffic at the pace you need by implementing a load curve that increases the number of simultaneous users, as necessary.

5. Execute Your API Load Tests

After configuring your load test, run the test. While it’s running, you’ll want to monitor any key performance indicators or metrics such as the response times and error rates. Over time, you should gradually increase the load to observe how the API behaves under stress.

6. Analyze Results

After your load test is completed, you can analyze the results of the test and evaluate your API’s performance against your predefined benchmarks/criteria. From here, you’ll be able to easily identify any bottlenecks, performance issues, or areas of improvement for your API. Using a tool like LoadView provides you with comprehensive reporting capabilities that lets you easily drill down your API’s performance metrics to quickly determine where you can improve and enhance your API for your users.

7. Iterate, Refine, and Integrate

Based on the analysis, refine your test scenarios, and address any issues discovered during testing. Iterate through the load testing process to continually enhance the API’s performance. From here, you will want to integrate your API load testing strategy with your CI/CD pipeline to ensure you discover any bottlenecks or issues early on. This will help you fix issues earlier and provide your users with a seamless experience using your APIs.

API Load Testing Best Practices

Here are some best practices to load test APIs:

  • Load test your APIs in a test environment but use real production data when testing. This ensures that you can fix any issues before it hits production, and the real data allows you to simulate real-world scenarios that your users would be performing.
  • Clearly define your benchmarks and criteria for your API performance. You should set your service level agreements (SLAs) to help provide you with a minimum level of performance requirement for your API calls. This is helpful when you’re testing because it allows you to test against those benchmarks. If any test fails to meet your expected SLAs, your APIs should view reviewed and improved to ensure that it’s up to standard.
  • Load test APIs early and often as possible. As you begin to load test your APIs, it’s important to integrate your testing strategy with your CI/CD pipeline. This ensures that tests are fun frequently in the initial stages of development and that any issues are caught before your APIs reach your production environment where your real users see them.

Load Test APIs with LoadView

Load testing an API with LoadView can be as simple as creating a script that sends several calls to the API in a sequence and scaling up the number of simultaneous users to the upper limits of expected traffic. The scripts are reusable and can be used to monitor the system throughout the service period.

Depending on the requirements of your API testing, the LoadView platform allows you to choose from multiple load curves. Define your API load tests to simulate traffic at the pace you need by implementing a load curve that increases the number of simultaneous users, as necessary.

Load Step Curve

  • The Load Step Curve option generates load with a pre-defined number of concurrent users, allowing you to check the response time as the number of concurrent users increases over a specified time.

Goal-based Curve

  • The Goal-based Curve allows you to automatically adjust users to reach the required rate of transactions. This type of test is typically used to validate Service Level Agreements (SLAs) in production environments.

Dynamic Adjustable Curve

  • The Dynamic Adjustable Curve allows you to change the user load, in real-time, during a test. You start with a pre-determined number of concurrent users and can be adjusted between a defined minimum and maximum.

LoadView also allows you to distribute the load between over 40 geographic regions in any manner that you want, and choosing the closest locations to your actual users will provide the most effective emulation of real users during a load test.

Take Your Concurrent User Testing to the
Next Level

Experience unparalleled features with limitless scalability. No credit card, no contract.