API Load Testing
Load test your REST, GraphQL, or other HTTP APIs from 32 AWS and GCP cloud regions. Identify scalability bottlenecks and find concurrency bugs before your users do. Record, import, or build a script with help from your favorite AI agent. Launch your first test and get actionable results in minutes!
API load testing hits your endpoints with many concurrent clients to measure throughput, latency, and error rates under pressure. Protocol Bots keep it lightweight, so a single test can push thousands of requests per second.
Load testing results without the endless configuration. Loadster's cloud testing platform helps you move faster: browser-based script recording, live test metrics, automatic reports.
Record test scripts
Record load test scripts right in your browser with the Loadster Recorder extension for Chrome or Firefox. Just navigate your site like a real user, while Loadster automatically records every action into a reusable test script.
Edit and replay scripts
Play scripts as often as you like in Loadster's script editor. Bots execute your script and give you immediate real-time feedback. In the editor you can add, edit, and replace steps from the recording, or you can even build a script from scratch.
Configure test scenarios
A scenario is a reusable configuration for a load test. You'll specify the number of bots in each group, the AWS or GCP regions bots will run from, which of your scripts to execute, and the schedule for ramping the load up and down.
Launch your load test
When you launch a load test from a scenario, Loadster quickly spins up cloud resources to power your bots. Tests usually start in about 2-3 minutes, using fully managed infrastructure through Loadster's AWS and GCP cloud providers.
Observe real-time results
While a load test runs, your bots report real-time metrics to Loadster, and Loadster surfaces the latest details and diagnostics within seconds. Keep tabs on response times, throughput, errors, and detailed traces so you can see how your site is performing under load.
Generate test reports
After a load test finishes, Loadster automatically creates a detailed report so you can review your site's performance and scalability. This includes detailed graphs showing response times, errors, network and transaction throughput, and more. The report also includes detailed traces with request and response bodies or screenshots to help with troubleshooting.
Repeat and iterate
Load testing is an iterative process, and it's rare that everything goes perfectly on the very first try. After all, the point of the test is to discover scalability bottlenecks so you can fix them instead of crashing in production. With Loadster you can quickly re-test a previous scenario, or make changes to your scripts or scenarios and run again at any time.
Protocol Bots, built for API testing at massive scale and reasonable cost. Loadster also has Playwright and Browser Bots for real browser load testing.
Protocol Bots
Protocol Bots send scripted HTTP/S requests straight at your API without rendering anything, so each bot is cheap to run and can drive a high request rate. A single test scales to hundreds of thousands of concurrent bots, which makes them the natural fit for REST and GraphQL APIs, microservices, and any endpoint where you care about requests per second, latency, and error rates rather than pixels.
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Browser Bots
Real headless Chrome browsers for web apps and modern websites. Record a script with the free extension and refine it in the web-based editor.
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Playwright
Run your Playwright Test scripts at scale, each in its own real browser, with Loadster's cloud scaling and reporting.
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Five ways to build a protocol script. Import what you already have, generate one from a spec, record it, build it, or let an agent write it.
Import from JMeter, k6, or Locust
If you've been testing with JMeter, k6, or Locust, bring your scripts! The importer accepts JMeter test plans, k6 scripts, and Locust files and quickly turns them into a protocol script.
Generate from an OpenAPI spec
Point Loadster at an OpenAPI (Swagger) definition and it generates the requests for you, so you start from a script that already knows your endpoints, methods, and parameters.
Record with the browser extension
If your API is called from a web front end, use the site normally with the free Loadster Recorder browser extension and Loadster records the underlying HTTP requests into a protocol script.
Build it in the web-based editor
Add your requests step by step, set headers and bodies, capture values from HTTP responses with capturing rules, and validate responses with validation rules. All in your browser, nothing to install.
Let your AI agent write it
Connect Claude, ChatGPT, or Cursor to your account through the Loadster MCP server. Describe the API flow and the agent writes the script, validates it, builds a scenario, and gets it ready for you to launch.
Performance engineering results with less time and effort. Loadster makes your team faster with browser-based scripting, fully managed infrastructure, live metrics, and automatic reporting.
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HTTP APIs
Build your test scripts as a sequence of HTTP requests, so you can test pretty much any API.
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Quick Editing
Edit your scripts and replay them with a single bot until it works perfectly... all from your browser.
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Instant Playback
As you play scripts from your web browser, watch the results in real time as each step runs. Edit and repeat as necessary!
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Diagnostic Traces
After your script runs, you can inspect requests, responses, screenshots, and errors from every step.
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Managed Cloud
No need install anything or set up test infrastructure! Loadster spins up fully managed cloud instances in about 2-3 minutes.
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Live Results
As each load test runs, keep an eye on the real-time graphs and tables. Observe your site's response times, throughput, and errors.
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Automatic Reports
Loadster automatically generates a full test report with charts and tables after each test. No more tedious manual reporting.
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Team Collaboration
Invite your colleagues, and anyone on your team can create scripts, run tests, and share results. Make scalability a team effort!
One protocol script for load testing, stress testing, and API monitoring. Same scripts, same platform.
The same protocol script can drive a full-scale load test, a stress test that pushes your API past its breaking point, or a 24/7 API monitor that alerts you the moment an endpoint slows down or starts returning errors.
Monitors run every minute, every five minutes, or whatever cadence makes sense. If a cycle fails (a timeout, a broken assertion, a page that didn't load), Loadster opens an incident and alerts your team by email, SMS, phone call, or your incident management integration.
Monitoring catches the problems that happen between releases. Load testing catches the ones that would have happened at peak traffic. Together they cover a lot of ground.
Web application load testing » Website stress testing » Synthetic monitoring »
Wire API load testing into your CI/CD pipeline. Test continuously to catch performance regressions before they reach production.
API load testing doesn't have to be a quarterly exercise. The Loadster CLI runs from your CI environment (GitHub Actions, GitLab CI, Jenkins, CircleCI, and others), so you can run a quick API load test on every pull request and a larger one with each formal deployment. Acceptance criteria such as response time thresholds and error rate ceilings can be encoded in the scenario, so the CI job fails automatically if performance regresses or the API load test detects errors.
For teams deploying daily, a 5-minute smoke API load test in CI can save you the grief of performance regressions reaching production. Set that up, then use the same scripts for the occasional larger test ahead of peak traffic events.
Load test your API on demand from 32 AWS and GCP cloud regions. Monitor continuously from 8 locations across 5 continents.
Loadster scales with your testing and your budget. Choose between flexible pay-as-you-go and predictable subscription pricing.
Monthly Fuel Plans
Starting at $77 a month
Subscribe to a monthly plan to automatically add fuel every month at a discount. Unused fuel rolls over as long as you keep the plan.
Check Plan PricingPay As You Go
Starting at $97 for 1000 units
Purchase as much Loadster Fuel as you need for your load testing and monitoring. No commitment, just buy it when you need it.
Check Fuel PricingFrequently Asked Questions
How does Loadster load test an API?
Can I import an OpenAPI or Swagger spec?
Can I load test authenticated APIs?
How much throughput can Loadster generate against an API?
Can I run API load tests in CI/CD?
Loadster has optimized the performance, scalability, and uptime of thousands of sites. We're proud to be a testing platform of choice to elite teams.
Move fast
Don’t crash
Ready to cut your risk of downtime? Load test to prevent crashes. Monitor to react quickly.