Send N concurrent requests, view average latency and error rate. Free online.
The HTTP Load Tester sends a configurable number of concurrent requests to a URL and reports success count, error count, and average (and sometimes p95) latency. Developers use it for a quick sanity check before deployment, to see how an endpoint behaves under a small burst, or to compare before/after a change. It is lightweight compared to full load tools; for sustained load or complex scenarios, use a dedicated load tool.
Browser-based tools are limited by connection limits; server-side tools may allow more. Check the tool's limits.
Any load can affect the server. Start with a small N and use a staging URL if possible.
Typically non-2xx status or network failure. The tool may list status codes and failure reasons.
Some testers allow custom method and headers; others only support GET to the URL.
Lightweight testers give a quick read; for stress or capacity planning use a proper load testing tool.