To stress test a site with Loader.io, register and verify its hostname, configure a test that reflects the traffic pattern you want to evaluate, then run it and inspect the results. Choose between distributed total clients, clients launched per second, and ramping concurrent load; these settings are not interchangeable. Only test systems you are authorized to load, and use a dedicated account if the scenario requires HTTP basic authentication.
What Loader.io does
Loader.io is a cloud-based load testing service for web applications and APIs. Its web interface and API support a workflow of registering a target host, verifying it, creating a test, running it, and reviewing or sharing results. Each unique hostname must be registered and verified independently, according to the Loader.io API documentation.
A load test can help reveal how an endpoint behaves under a specified traffic pattern. It does not, by itself, establish a universally safe user limit or prove that a host may be tested. Coordinate the run with the people responsible for the application and infrastructure.
Choose the traffic pattern that matches your question
Loader.io documents three test types. Pick one according to whether you want to control total volume, arrival rate, or concurrent load.
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| Test type | What the setting controls | Useful for asking |
|---|---|---|
| Clients per test | Distributes the specified total number of clients over the test duration. | How does the target behave as a given volume of clients is spread across this time window? |
| Clients per second | Starts the specified number of clients each second. | How does the target respond to a specified client arrival rate? |
| Maintain client load | Ramps concurrent clients from a starting value to an ending value; each client continues making requests. | How does the target behave as concurrent load rises or is sustained? |
These settings describe different traffic patterns, not equivalent ways to enter the same number. Loader.io’s Help Desk illustrates the distinction with a 20-second test: 20,000 clients per test distributes 1,000 clients per second, while a clients-per-second test configured for 1,000 also starts 20,000 clients in total over 20 seconds. Actual active concurrency can differ, especially in a clients-per-second test, because response times affect how long clients remain active. The example comes from an article last updated December 1, 2020; check the current interface for its terminology.
Register and verify the target host
- Add the hostname: Register the host you intend to test before creating a test. Register each unique hostname separately.
- Complete verification: Verify the hostname through Loader.io’s process. Do not assume that registering one hostname verifies other hostnames belonging to the same site.
- Confirm authorization and coordination: Make sure you have permission to generate the planned traffic and that the application and infrastructure owners know when the test will run.
Configure a realistic test
After verification, create a test and specify the endpoint scenario. Configure the URL or sequence of URLs, request method, and any headers, parameters, payload, raw body, or response variables the scenario requires. Then choose a duration and set the client count according to the selected traffic pattern. A single URL request may not represent a workflow that depends on multiple requests or particular request data, so model the behavior relevant to the question you are testing.
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Set timeout and error threshold deliberately
The Loader.io Help Desk’s Creating a Test article describes a 10-second timeout default. The API v2 documentation lists a default timeout of 10,000 milliseconds and a default error threshold of 50 percent. These are product defaults, not universal recommendations. Set them to fit the test objective: the timeout affects how long a request may take before it is treated as timed out, and the threshold can automatically abort a test after the configured error percentage is reached.
Loader.io’s API documentation says a test starts automatically when it is created unless it is scheduled. Check the scheduling and run settings before saving if you are not ready for traffic to begin.
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Protect credentials used by an authenticated test
Loader.io’s Creating a Test article warns that HTTP basic-auth credentials are stored unencrypted on its servers, explaining that they must be available for use during the test. If authentication is necessary, create a dedicated test user with only the access required for the scenario. Avoid entering sensitive production credentials casually.
Check account limits and current pricing
Maximum test duration depends on the account, subscription, or add-ons, according to Loader.io’s API documentation. The service’s current pricing information presents plan-specific duration and capacity, with prices excluding VAT. Because limits and prices can vary by plan, account, and location and can change over time, confirm the live offer and your account’s limits before scheduling a long or high-volume test.
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Loader.io’s service page markets “thousands of concurrent connections,” but that is vendor positioning, not an independent benchmark. The cited product information does not establish a universal maximum load that a particular application can safely handle. Use results from a controlled test of your own authorized target rather than treating a service setting or marketing statement as a capacity guarantee.
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After the run, inspect the results against the question you chose at the outset. A test configured by total clients answers a different question from one configured by arrivals per second or by ramping concurrency. Interpret errors and timeouts in light of the chosen threshold, timeout, request sequence, and duration; a test with a different configuration is not a like-for-like comparison.
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Loader.io offers result review and sharing, as well as a web interface and API workflow. The cited documentation does not establish an independent benchmark of Loader.io’s performance or a full comparison with other load-testing approaches.
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