Locust is an open-source, developer-friendly load testing framework written in Python. It allows users to define test scenarios as regular Python code using `User` classes with `@task` decorators and configurable wait times. The system supports HTTP and other protocols via built-in clients (HttpUser, FastHttpUser) and extensible contrib modules (MQTT, gRPC, Postgres, etc.). It provides a real-time web UI built with React/Redux/MUI for controlling tests and viewing statistics, a headless CLI mode for CI/CD integration, and a distributed architecture using ZMQ for master/worker coordination. The framework collects detailed per-request metrics (response times, percentiles, error rates) and can export CSV, HTML, and JSON reports. It also integrates with OpenTelemetry for observability. The codebase is well-structured with a clean event-driven architecture, extensive test coverage, and a plugin system for custom extensions.