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Performance Testing Tools for UI

Performance testing, also known as load testing, or stress testing, is an important part of web site and web-based application development. It assures that the software can handle a specific number of concurrent users and/or Web sessions without crashing.

Get Best Performance Testing Tools in Software testing which are used to test performance of software, websites and other applications mainly by providing tools to check system’s standard performance metrics such as reliability, scalability, and efficiency.

What is load testing?

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 performance.

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 behave properly under heavy load
  • Is your infrastructure designed to scale under stress

Performance testing in general is critical to customer satisfaction. If your application performance doesn’t meet the expectations of your customer, they will move on to your competitor.


In fact, load testing 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 are is our comprehensive list of the top open-source and FREE performance load testing tools you can use for your load and stress testing performance engineering efforts.

Below are some options that include a tool comparison to help you make your decision on what tool to use for your application performance efforts in 2021.

Performance Test Tool

The Top Load Testing Tools List for 2021

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

JMeter jmeter

JMeter is the most popular open-source tool 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 pretty much be the open-source alternative to LoadRunner, so you’ll find it has lots of 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.

Some features are:

  • 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, 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 performance testing tools
  • Can configure it to help test mobile performance of mobile apps

Github starsIt currently has 5.1k stars on GitHub.

Although JMeter is one of the more popular test tools, it does have some shortcomings.

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.

Taurus Taurus

While not technically a load testing tool Taurus acts more like a wrapper on top of other solutions that hides 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, which gives teams the ability 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 big, heavy vendor-specific record and scripting tool for load time measuring.


  • This should also allow more members of your team 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 on.
  • Taurus basically fits performance testing into your CI/CD pipeline much more efficiently.
  • Taurus provides a sort of abstraction layer on top of JMeter, as well as some other tools like Locust, Gatling, the Grinder and Selenium.

Github starsIt currently has 1.4k stars on GitHub.

Locust Locust

Locust is a simple-to-use, distributed, user load testing tool that can help you capture response times.

What scripting languages does it use? The best one — Python! 🙂

It is used to helps performance test websites or other applications.

Locust can also help you figure out how many concurrent users a system can handle.

Where tools like jMeter are based upon, a thread-based architecture that consumes a lot of resources. 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.

Some of the cool key features you get with Locust are:

  • 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


Since its a newer tool it has far fewer plugins than JMeter

Github starsIt currently has 15.7k stars on GitHub.

Performance Testing Tutorial | TestGuild

Fiddler with BlackWidow and Watcher svg+xml;nitro-empty-id=OTA3OjIxOQ==-1;base64,PHN2ZyB2aWV3Qm94PSIwIDAgNTAgNTAiIHdpZHRoPSI1MCIgaGVpZ2h0PSI1MCIgeG1sbnM9Imh0dHA6Ly93d3cudzMub3JnLzIwMDAvc3ZnIj48L3N2Zz4=

This might seem like an odd combination to have on a 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.

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.

Some things you might want to use Fiddler for:

  • 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 is sending to a service or website.

Watcher is a security add-in for Fiddler which will enable 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 who’s just getting started in performance engineering, these three tools working together can provide a great way to get that free look and feel as well as results that one might not otherwise be able to obtain quickly.

Todd actually has a session during a past PerfGuild Online Conference where he gives a demo of this approach.

nGrinder Grinder

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


  • 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

Github starsIt currently has 1.3k stars on GitHub.

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 users restrictions.

  • 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


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

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

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

Github starsIt currently has 5.1k 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.


k6 is a developer-centric, open-source load testing tool for testing the performance of your back-end infrastructure.

You can also use k6 to start including performance testing into your continuous integration pipelines.

k6 is also  Modern load testing tools built with Go and JavaScript so it integrates well into most developers’ workflow.

  • Clean scripting API
  • Provides distributed & Cloud execution
  • Cool REST API orchestration ability

Github starsIt currently has 11.7k stars on GitHub.


Tsung is an open-source, multi-protocol distributed load testing tool.

  • Can monitor a client’s CPU, memory, and network traffic
  • It has an HTTP recorder
  • Includes HTML reports and graphs
  • Support protocols like HTTP, XMPP, LDAP, etc.

Github starsIt currently has 2.1k stars on GitHub.

Siege Siege

Siege is a command-line HTTP load testing and benchmarking utility. It was designed to help developers measure their code under stress.

  • Supports basic authentication, cookies, HTTP, HTTPS and FTP protocols.
  • Allows its users hit a server with a configurable number of simulated clients. Those clients place the server “under siege.”
  • Great for a simple, brute-force type of testing tool

Github starsIt currently has 4k stars on GitHub.

Bees with Machine Guns bees with machine guns

Developed by the Chicago Tribune, this is probably the coolest-sounding performance testing tools on this list.

Bees with Machine Guns describes itself as a utility for arming (creating) many bees (micro Amazon EC2 instances) to attack (load test) targets (web applications).

This tool can easily help you load test a site that needs to handle high traffic.

Leverage Amazon EC2

It currently has 6k stars on GitHub.

For enterprise-wide performance testing tools, LoadRunner tends to be one of the most common but many of these open-source tools can get you most of the functionality you need. Also, most of these tools protocols can be used for both performance testing web application and performance testing web services.


Fortio is a cool load testing library, command-line tool, advanced echo server and web UI in go (golang).

This tool allows to specify a set query-per-second load and record latency histograms and other useful stats.


  • It’s fast
  • Small footprint (3Mb docker image, minimal dependencies)
  • Reusable
  • Embeddable go library
  • Can tecord latency histograms and other useful stats.
Github stars

It currently has 1.8k stars on GitHub.


The Complete Front-End Performance Testing Guide

With most modern applications using javascript heavy front-ends the needs for client-side performance measurements have never been greater.

Don’t ignore front-end performance.

You can use Puppeteer WebPerf to collect web performance stats like a trace for a page load, grab a dev tools trace with screenshots, get runtime performance metrics, and a bunch more.

Also, check out my complete front-end performance testing guide for more info.

Github stars

It currently has 1.4k stars on GitHub.

Flood Element

Want to test real browser load?

Flood created this open-source solution to help specifically with mimicking user behaviors using real browser load testing.

Element is an open-source Playwright that uses a browser-based load testing tool.

Scripts are created using Typescript.

You can use it against your Web app in the same way that your customers do, opening a browser and interacting with page elements.

This approach can help find user-facing performance issues.

It’s written like a functional test script, but with the help of Flood, you can quickly run load testing scripts on as many nodes as you want in the Cloud.

One of the few open-source tools that allow you to create performance testing using real browsers to more closely mimic how real users interact with your application.

Read about it in my post Browser Level Performance Testing Using Element.

Github stars

It currently has 204 stars on GitHub. is an open-source application with an opt-in of premium services to create load tests to simulate load to emulate thousands of users.

It has detailed performance metrics including:

  • latency
  • requests per second
  • concurrency
  • capture average response time
  • and throughput.

Peak performance testing to handle maximum traffic for your back-end application for stability and reliability.

It has the ability to write custom logic, post, and pretest scenarios using JavaScript, which has a wide variety of NPM modules that you can use.

It supports multiple protocols, including HTTP, Web Socket, Socket.IO, Kinesis, and HLS.

Github stars


Performance Testing is a broad concept that incorporates the testing of an application’s behavior. Many people think it is only about checking how fast an application performs. This, in fact, is just one dimension of performance and the reason why people tend to mistake it for Load or Stress Testing – these tests are specifically designed to see how particular system outperforms or breaks under high load circumstances. For example, a company may use different types of applications and software packages (such as ERP, CRM, accounting systems) to organize their business operations more effectively. Now each of these applications has its own set of features and usually users don’t know much about process flow – they just know what to do for a given task when required by their manager or CIO. So computers are used for specific purposes such as processing and storing information, which leads to a large set of computer programs and their functions. Consequently, this results in many cases in using more than one software package on a single PC – for example if you have installed MS Office on your computer and you need to buy something from Amazon, you will probably do it with your web browser (Chrome or IE), but at the same time you will use your email client (such as Outlook) to

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