API Load Testing

Load test your REST, GraphQL, and HTTP APIs with thousands of lightweight protocol bots across 32 cloud regions. Import a spec or script it by hand, then run a test and get your first results in minutes.

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.

1

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.

2

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.

3

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.

4

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.

5

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.

6

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.

7

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.

Load Test Your API

Protocol Bots, built for APIs. Lightweight HTTP clients that push high throughput at low cost.

API load testing doesn't need a browser. Loadster's Protocol Bots send requests straight at the HTTP layer, so each bot is cheap to run and can drive a high request rate. That makes Protocol Bots ideal for REST and GraphQL APIs, microservices, and high-throughput endpoints, where you care about requests per second, latency, and error rates rather than rendering a page.

Testing a browser-based front end too? Loadster also runs real-browser Playwright and Browser Bots, and you can mix bot types in a single test to model a complete system end to end.

Load Test Your API

Start from your OpenAPI spec, or script it yourself. Turn an API definition into a load test in minutes.

Already have an OpenAPI (Swagger) definition? Loadster can generate a protocol script from it, so you don't have to write every request by hand. From there you parameterize requests, add authentication, and chain calls into realistic workflows.

Real API workloads are rarely a single endpoint hit in a loop. Protocol scripts let you log in and capture a token, feed unique values from a dataset into each bot, extract values from one response with code blocks and pass them to the next request, and assert on status codes and response bodies — so every bot behaves like a different real client.

Measure latency, throughput, and errors under load. Live metrics from every bot, aggregated in real time.

Loadster reports response times with full percentiles (50th, 90th, 95th, and 99th), requests per second, and error rates for every endpoint in your script, updating live as the test runs. When throughput plateaus while concurrency keeps climbing, or the 99th percentile starts to spike, you've found the point where your API begins to strain — and traces on failed requests show you the exact call and response that broke.

Load Test Your API

One script for load testing, stress testing, and monitoring. Write your API test once and reuse it.

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 runs on a schedule and alerts you the moment an endpoint slows down or starts returning errors.

Run API load tests in your pipeline. Catch performance regressions on every deploy.

The Loadster CLI runs from any CI environment — GitHub Actions, GitLab CI, Jenkins, CircleCI — so an API load test can run automatically on every pull request or deploy. Encode response time and error rate thresholds in the scenario, and the job fails automatically when your API regresses.

Load test your API from 32 cloud regions across AWS and GCP clouds. Monitor from 8 dedicated locations on 5 continents.

Loadster scales with your testing and your budget. Choose between flexible pay-as-you-go and 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.

Plan Pricing

Pay 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.

Fuel Pricing

Frequently Asked Questions

How does Loadster load test an API?
Loadster drives your API with Protocol Bots — lightweight HTTP clients that send requests directly at the protocol level, with no browser. Each bot runs your script (a sequence of API calls with headers, authentication, and assertions) concurrently, so you can push a high request rate and measure how your API responds under load.
Can I import an OpenAPI or Swagger spec?
Yes. Loadster can generate a protocol script from an OpenAPI (Swagger) definition, so you can turn an existing API spec into a load test without writing every request by hand. From there you can parameterize requests, add authentication, and chain calls together into realistic workflows.
Can I load test authenticated APIs?
Yes. Protocol scripts can perform a login or token request, capture the returned token or session cookie, and pass it into the requests that follow. Bearer tokens, API keys, OAuth flows, and custom headers are all supported.
How much throughput can Loadster generate against an API?
Protocol Bots are lightweight, so a single bot can drive many requests per second and a test can scale to thousands of concurrent bots across 32 regions. Protocol testing reaches far higher throughput per bot than browser-based testing, which makes it well suited to API and other high-throughput load testing.
Can I run API load tests in CI/CD?
Yes. The Loadster CLI runs from any CI environment, so API load tests can run automatically on every deploy or on a schedule, with pass/fail thresholds for response time and error rate encoded in the scenario.

Loadster has improved the performance, scalability, and uptime of thousands of sites. We're proud to be of service to the best teams.

  • Nginx
  • Wells Fargo
  • Amazon
  • Queensland Government
  • Accenture
  • Yale University
  • HBO
  • Mint Mobile
  • KPMG
  • Perficient
  • Dell
  • Pearson

Move fast
Don’t crash

Ready to cut your risk of downtime? Load test to prevent crashes. Monitor to react quickly.

Load Test Your API