15 Top Load Testing Software Tools for 2025

In the world of software development, testing is vital. No matter how well you code or how thorough your initial testing process may be, there’s always a chance that something will slip through the cracks.

That’s why load testing is so important. And while plenty of commercial tools out there can help you with this process, open-source load testing software is also available

In this guide, you’ll learn:

• The importance of load testing
• Top open-source and FREE performance load testing tools for your load and stress testing performance engineering efforts
• Some key features of each load testing software

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Why is it important to incorporate load testing early and regularly in software testing practices?

Load testing is a specific sub-family of a performance test that includes many concurrent users running the same program at the same time. This is done to see whether a system infrastructure can handle the load without compromising functionality or just with acceptable performance degradation.

Load testing is used to help determine if:

• The response time returned from critical actions in your application is acceptable compared to specification, user requirements, or KPI.
• Are your key business functionality behaving properly under heavy load
• Is your infrastructure designed to scale under stress tests

Front-end performance testing measures how fast your website loads and displays content for users. In contrast, back-end performance testing involves sending multiple requests to your servers to see if they can handle simultaneous requests. Most performance testing tools only test API endpoints, but tools like xk6-browser go beyond that by testing browser performance as well.

Performance testing tools, in general, are critical to customer satisfaction. They will move on to your competitor if your application performance doesn’t meet your customer’s expectations or all service level agreements.

Is load testing considered non-functional or functional testing, and why?

Load testing is typically considered a non-functional type of testing because it focuses on testing performance, reliability, and resource usage characteristics rather than particular functions or user stories.

However, poor performance directly impacts user experience and can render an application effectively unusable, so organizations shouldn’t consider performance as purely non-functional. There is overlap with functional testing, especially for catching issues like race conditions or resource leaks that only manifest under load.

The best approach is to incorporate load testing alongside functional testing in an integrated manner to build an overall quality product. Dedicated load testing is still needed to stress the system and find limits.

Start Load Testing Early

Incorporating load testing early and regularly in software testing practices is crucial for several reasons.

Firstly, load testing allows software developers to evaluate how a system functions under high-stress conditions, such as when multiple users are simultaneously accessing an application.

By conducting load testing early in the development process, potential performance bottlenecks and scalability issues can be identified and addressed proactively before they impact end users.

This proactive approach not only helps in delivering a reliable and efficient software product but also enhances the overall user experience.

Additionally, even smaller applications can benefit from load testing as it provides valuable insights into their performance capabilities and limitations under stressful situations. Regular load testing helps in maintaining and improving the performance of the software, ensuring it can handle real-world usage scenarios effectively.

Load testing should be incorporated from the early stages of development and done regularly, not just before major launches or when issues arise. Key reasons include:

• Detect performance issues early before they impact real users. Don’t wait for user complaints.
• Understand the performance profile and set baseline metrics to catch regressions over time.
• Ensure the application remains performant as new features are added.
• Allow time to optimize and fix issues. Performance shouldn’t be an afterthought.
• Build a performance culture where it’s everyone’s responsibility.

Load Testing vs. Other Test

Load testing vs. other tests is one of the most misunderstood parts of performance testing. And there are many load testing best practices you should be aware of before even using one of the tools listed below.

Here is our comprehensive list of the top open-source and FREE load testing tools you can use this 2024 for your load and stress testing performance engineering efforts.

Below are some of the best load testing tools that include a tool comparison to help you decide on which one is right for your application performance efforts in 2025.

The Top Load Testing Tools List for 2025

This list only includes open source and free options for the top load test software for automated performance testing and API load tests, so you can just download and get started right away without spending a dime.

* But before we get to the free options, if you are serious about reliable enterprise-wide performance load testing, then you need a vendor-based solution. Trust me—I started my career as a performance tester and would not have been able to do my job without a full-scale solution like WebLOAD.

1. JMeter 

JMeter is the most popular open-source load test software in the performance space to help measure load time.

Apache JMeter describes itself as a Java application that was designed specifically for load testing with the ability to measure application performance and response times.

JMeter was built to be the open-source alternative to LoadRunner, so you’ll find it has many sophisticated features. It’s a thick client Java app that’s largely driven by right clicks. It’s a little weird, but it’s got a lot of power. Also, all the features a professional load tester wants are available on JMeter.

Key Features

• The ability to performance test a host of technologies using a range of protocols such as Java Objects, Web HTTP/HTTPS, SOAP and Rest Services, FTP, and Databases with JDBC
• A nice IDE you can use for recording, building, and debugging your performance tests.
• Starting with JMeter 3.1, Groovy is the default programming language
• One of the more popular load testing tools
• Can configure it to help test the mobile performance of mobile apps
• Using jmeter-java-dsl, you can write your performance tests in Java and take advantage of IDEs autocompletion and inline documentation.

It currently has over 8.7k stars on GitHub.

Cons

Although JMeter is one of the more popular load testing tools, it does have a breaking point, such as:

For instance, JMeter can be a bit difficult to scale for a large distributed test, especially if you have to set up a bunch of machines since you have to configure them to talk to each other. There is also a host of orchestrating problems in executing large JMeter tests.

That’s where a tool open–sourced by BlazeMeter—Taurus—can help you out.

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2. Taurus

While not technically a load testing tool, Taurus acts more like a wrapper on top of other solutions that hide the complexity of running performance tests.

The power of Taurus is that it allows you to write your tests in YAML.

You can actually describe a full-blown script in about ten lines of text, allowing teams to describe their tests in a YAML or JSON file. The YAML is a human, readable, edible approach that enables you to describe a test in a simple text file.

This is a big leap forward from the old days of having to bring up a significant, heavy vendor-specific record and scripting tool for load time measuring.

Key Features

• This should also allow more team members to contribute to performance tests. Also, since your test cases are written in YAML, the tests are much more readable, making them easier to perform code reviews.
  
• Taurus basically fits performance testing into your CI/CD pipeline much more efficiently.
• Taurus provides an abstraction layer on top of JMeter and some other tools like Locust, Gatling, the Grinder, and Selenium.

It currently has 2.1k stars on GitHub.

3.Locust 

Locust is a simple-to-use, distributed, user load testing tool that can help you capture response times. So, what scripting languages does it use?

The best one — is Python. It is used to help performance test websites or other applications.

Locust vs. JMeter

Tools like JMeter are based upon a thread-based architecture that consumes many resources. On the other hand, Locust uses an event-based approach that uses fewer resources.

Rahul Solanki, a technical leader at BlueConch Technologies, mentioned to me that when he compared it with JMeter, the number of resources that Locust occupies was around 70 percent less.

If you’re familiar with the term “load generators,” Locust uses the term “swarm”–as in you can point a swarm of locusts to put a load on your website.

You can define the behavior you want for each of your Locust instances. It also gives you the ability to monitor the swarming process from a web UI in real-time.

Key Features

• The ability to create your test scenarios using straight Python
• You can easily scale the number of users you need to emulate
• It has a nice Web-based UI
• Extensible
• Good for testing APIs

Cons

Since it’s a newer tool, it has far fewer plugins than JMeter.

It currently has 25.9k stars on GitHub.

4. Fiddler with BlackWidow and Watcher 

This might seem like an odd combination on a website performance tool list.

But performance engineering expert Todd DeCapua, in a previous PerfGuild conference session, recommended using Fiddler with Watcher and BlackWidow to create a quick-start automation testing performance solution.

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Fiddler enables you to do many things, but it’s probably best described as a packet capture tool.

While Fiddler may not be considered a load testing solution, it does many things that allow you to debug website issues, and with one of its many extensions, you can accomplish even more.

Key Features

• Troubleshooting issues with your web application
• Security testing
• Performance evaluations
• Debugging web traffic from most computers and devices
• Many integration features
• Handy for finding performance bottlenecks
• Fiddler is already a pretty popular tool among developers. Many use it for debugging to view the HTTP requests their computer sends to a service or website.

Watcher is a security add-in for Fiddler, enabling you to get some security results quickly. BlackWidow is a web crawler that gives you the functionality to point it towards a web address and then be able to drill down on results.

For someone just getting started in performance engineering, these three tools working together can provide a great way to get that free look and feel and results that one might not otherwise be able to obtain quickly.

Todd had a session during a past PerfGuild Online Conference where he demoed this approach.

5. nGrinder 

nGrinder‘s GitHub page describes it as having been designed to be an enterprise-level performance engineering solution. It was developed to simplify stress testing and provide a platform that allows you to create, execute, and monitor tests.

Key Features

• You can write your tests using Jython or Groovy to create test scenarios and create stress against JVM using multiple agents.
• It can extend tests with customer libraries like jar and py
• Allows you to monitor the state of your performance agents load generation
• Take care of automatically collecting test results from distributed agents after tests

It currently has 2.1k stars on GitHub.

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6. The Grinder

The Grinder is a Java-based framework. It provides you with easy-to-run and -create distributed testing solutions using many load generator machines to capture your end-users response times. So you don’t have to worry about any virtual user restrictions.

Key Features

• You can perform load testing on any system that has a Java API
• A nice GUI console
• It automatically handles the management of client connections and cookies 

7. Gatling

Gatling is a stress test tool built on Scala, Akka, and Netty.

This modern architecture approach allows you to test and measure your application’s end-to-end performance and easily scale up your virtual users’ to-end performance and easily scale up your virtual users.

Key Features

• It has a simple yet powerful DSL.
• Easy to extend
• If you’re into Scala and its benefits, this is the best load testing tool for you.
• It has a scenario recorder.
• Allows you to take a shift-left code approach to performance testing

Two major Updates: Gatling recently announced is has launched a new JavaScript and TypeScript SDK, doubling its accessibility for developers. It also has introduced enhanced no-code testing capabilities in their latest update. The new features aim to make performance testing more accessible by allowing users to create and execute tests without needing to write code.

It currently has 6.6k stars on GitHub.

To learn more about Gatling, check out the Founder of Gatling, Stephane Landelle’s PerfGuild session on Load Testing Done Right with Gatling.

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