The best load testing tool depends on how you like to work: an open source framework suits developers who write tests as code, a cloud service suits quick checks of an endpoint, and an enterprise platform suits complex apps. Ten options follow in no particular order.
Load testing sends lots of pretend users at your site or API to see what happens when traffic spikes. It answers the question every business with a launch, a sale or a big campaign should ask: will it stay up when people turn up in numbers?
The ten tools below are listed alphabetically and in no particular order, from free frameworks to platforms that generate tests for you. Every description comes from the vendor's own site, read this week. If you're wondering how speed affects results, my piece on how website performance affects your results explains the link.
Load testing tools at a glance
In the free plan column, Yes means the tool's own site names a free plan, a free version, a free tool or an open source edition. Trial only means a time-limited trial. Not stated means the pages I read named neither, even where there's a button inviting you to try it.
| Tool | Type | Good for | Free plan |
|---|---|---|---|
| Apache JMeter | Open source load testing application | Simulating heavy load on servers | Yes |
| Artillery | Performance and reliability toolkit | Load tests plus Playwright browser tests | Not stated |
| BlazeMeter | Performance and API testing platform | Generating tests from described journeys | Not stated |
| Gatling | Load testing with a test-as-code approach | Load tests written as code | Yes |
| Grafana k6 | Load testing for engineering teams | Fitting load tests into Grafana | Yes |
| Loader.io | Free cloud load testing service | Quick stress tests of an API endpoint | Yes |
| LoadNinja | Browser-based load testing tool | Load testing without writing scripts | Trial only |
| Locust | Open source load testing framework | Writing user behaviour in Python | Yes |
| RedLine13 | Cloud load testing on your own account | Running open source tests in the cloud | Not stated |
| Tricentis NeoLoad | Enterprise performance testing platform | Performance testing in enterprise pipelines | Not stated |
Ten load testing tools to consider
Apache JMeter
Best for: Teams that want a free, open source Java application to simulate heavy load on a server, group of servers or network.
Artillery
Best for: Developers who want load testing, scalable Playwright end-to-end tests and production checks in one toolkit.
BlazeMeter
Best for: QA teams that want to describe user journeys and goals and have performance tests generated and run for them.
Gatling
Best for: Engineers who want load tests written as code, with an open source community edition and an enterprise option.
Grafana k6
Best for: Engineering teams that want open source load testing that fits into Grafana dashboards, with a cloud service too.
Loader.io
Best for: Developers who want a free cloud service to stress test a web app or API endpoint with thousands of connections.
LoadNinja
Best for: Businesses without performance specialists who want load tests in real browsers with no coding, plus a free trial.
Locust
Best for: Python developers who want to define user behaviour in code and swarm a system with simultaneous users.
RedLine13
Best for: Testers who already write JMeter, Gatling or Selenium tests and want to run them at scale in the cloud.
Tricentis NeoLoad
Best for: Enterprises that want AI-powered performance and load testing across complex apps from a large testing vendor.
Code-first, browser-based or cloud service?
Code-first tools let you describe user behaviour in a script, keep it in your repository and run it in your pipeline. They're popular with developers and often open source. Browser-based tools replay real browser sessions, which is closer to what users see but heavier to run at scale. Cloud services take care of the machines that generate traffic, so you can test from outside your own network.
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You'll often use more than one: a simple cloud check before a launch, and code-based tests that run every week.
Test past your busiest day
The GOV.UK Service Manual says load tests should include loads in excess of your expected traffic levels, and that you should gradually increase the load until the service breaks in some way and your monitoring tools alert you.
That's the point many teams miss. A test that stops at expected traffic only tells you that you're fine on a normal day. Finding where it breaks, and how, tells you what to fix before the day that isn't normal. One more tip from government practice: GOV.UK Pay's own documentation asks teams to get approval before performance testing against it, so check the rules of any third-party service your test will hit.
Questions to ask before you choose
- Do we want to write tests in code, or record them?
- Will we test APIs only, or full pages in real browsers?
- Can we run tests from outside our network?
- Does it plug into the monitoring we already use?
- Can tests run automatically in our pipeline?
- Which third-party services will the test touch, and do they allow it?
What to watch during a test
- Response times. Look at the slowest users, not just the average.
- Error rates. A fast error is still an error.
- Database load. It's often the first thing to struggle.
- Third-party calls. Payment and email providers have their own limits.
Do you make load testing tools? Tool makers can ask to be considered for a featured place on this list.
My plain advice on load testing
Test the journey that makes you money, not just the home page. A home page can be served from a cache all day while the checkout or sign-up form falls over. Script that journey, run it in a test environment, and raise the load gradually until something gives.
Write down what broke and at what point, then fix the weakest link and test again. Repeat before every big launch. My guide to the ecommerce metrics worth tracking helps you decide which journeys matter most.
Frequently asked questions
What is load testing?
It's testing how a website, app or API behaves when many users arrive at once, so you can find slowdowns and failures before real users do.
What's the difference between load testing and stress testing?
Load testing checks behaviour at expected and higher traffic. Stress testing pushes past that until something breaks, to see how it fails.
Are there free load testing tools?
Yes. Several tools in the table name an open source edition or a free service on their own site. Check the free plan column for each one.
Can I load test someone else's service?
Only with permission. Testing a service you don't own can look like an attack, and some providers ask you to get approval first.
Should I load test production?
GOV.UK guidance points teams to test environments. If you must test live, do it at a quiet time with everyone warned.
How often should I run load tests?
Before any big launch or campaign, and regularly as part of your pipeline so performance problems don't creep in unnoticed.
