Send a request, run a load test, and get a plain-language answer: is your API fast enough, and will it hold up? No scripts to write, no account, and your tests never leave your computer.
Load tests run on k6, the open-source load-testing engine — packaged inside the app, nothing to install or configure.
Everything you need to know if your API is ready
Built for developers and testers — and readable by everyone else on the team.
Answers in plain words
“Meets your goals under this load” instead of a wall of numbers. Every term has a plain name, with the technical one beside it.
Send and load test in one place
Paste a URL or a curl command, check the answer, then run it with hundreds of simulated users — same request, one click.
Reports you arrange yourself
20 charts and numbers to choose from. Drag, resize, and save your own views — one for developers, one for managers.
Real-world tests
Sign in first and reuse the token, feed in users or IDs from a CSV file, set pass/fail goals, and check every answer is correct.
See if it got faster or slower
Every run is kept. Pick a reference run and later runs show the change. Compare several APIs side by side under the same load.
Private by design
Runs from your computer, so it reaches localhost and internal APIs. Results are plain files you own; saved secrets are encrypted.
From URL to answer in three steps
New to load testing? A built-in practice API and a one-minute tour get you started safely.
Step 1
Send one request and check it works
Paste a URL — or a whole curl command from your browser — and press Send. Add checks like “status is 200” or “has a name field” so a fast-but-wrong answer still fails.
Step 2
Run it under load
Choose a preset — smoke, average day, stress, spike, or soak — or set your own users and duration. Watch response time and requests per second live.
Simulated users, or a fixed request rate
Step-by-step ramps for real traffic shapes
Stops early if a goal is clearly missed
Step 3
Read it, shape it, share it
Get a plain result first, then the detail. Rearrange the report into your own view and export it as Excel, HTML, or JSON — or email a summary.
Beyond the basics
Sign in first, then test
Most real APIs need a token. Pick your sign-in request under Run first, choose the value to keep, and use it as {{token}} — on Send and for every request of a load test.
Download APITestCenter
Free for Windows 10 and 11 (64-bit). No account, no sign-up.
Installer
Installs for your user account with a Start menu shortcut. Recommended.
Windows may say “Windows protected your PC”. That happens with new apps that are not yet code-signed. Choose More info → Run anyway. Signing is on the way.
Yes. Sending requests, load tests, reports, history, and the command line are free. A paid Pro edition with extras for teams may come later; the free features stay free.
Does it send my requests or results anywhere?
No. Requests go straight from your computer to the API you are testing. Results are saved as plain files on your computer, which you can open, move, or delete. The app has no account and collects no usage data. See the privacy page.
Can I test APIs on localhost or my company network?
Yes — because the app runs on your computer, it reaches anything your computer can: localhost, VPN, and internal services. Online load-testing services cannot.
I have never done load testing. Where do I start?
Open the app and choose “Try a simple request”. It uses a small practice API built into the app, so you can learn without touching a real system. The one-minute tour and the Help panel explain every term in plain words.
How many users can it simulate?
Up to 500 simulated users, or a fixed rate of up to 100,000 requests per second — limited mostly by your computer and network. The report shows when the machine itself was the bottleneck.
Can I use it in CI?
Yes. The atc command runs a saved request's load test without the window and writes JUnit, JSON, or HTML reports. It exits with an error when a goal is missed.
Is it safe to load test any API?
Only test systems you own or have permission to test. A load test is real traffic; against someone else's API it can look like an attack.
APITestCenter
