Locust

Locust is an open-source performance and load testing tool for HTTP and other protocols. Tests are defined as ordinary Python code, so you can use loops, conditions and any Python library, and your design is never restricted by a GUI or a domain-specific language. It is released under the MIT license. Scenarios can be edited in a normal IDE and kept under version control like other code.

Locust runs each simulated user in its own greenlet, so tests read like blocking code instead of callbacks. It is event-based using gevent, which lets a single process handle many thousands of concurrent users, and load tests can be distributed over multiple machines. You can run it from the command line or through a web interface that shows throughput, response times and errors in real time, with data exportable for later analysis. A pluggable architecture lets you extend it.