API load testing: A beginner's guide

API load testing is a structured process that begins with small, isolated tests and evolves into comprehensive strategies assessing API performance under various conditions. It involves scripting user flows, setting parameters, and grouping URLs to assert performance and correctness. Load is modeled using virtual users or requests per second, with sleep time added to simulate real-world traffic patterns. Tests are designed to verify application responses and ensure they meet service level objectives (SLOs) through thresholds. Error handling and test modularization are critical to managing large-scale tests, and tools like k6 can be used alongside converters and proxy recorders to automate and expand testing capabilities. Although primarily focused on HTTP APIs, k6 also supports protocols like WebSockets and gRPC, with extensions available for additional protocols, allowing for comprehensive performance testing across various systems.