An open source load testing tool.

Define user behaviour with Python code, and swarm your system with millions of simultaneous users.

Define user behaviour in code
No need for clunky UIs or bloated XML. Just plain code.
Distributed & Scalable
Locust supports running load tests distributed over multiple machines, and can therefore be used to simulate millions of simultaneous users
Proven & Battle-tested
Locust has been used to simulate millions of simultaneous users. Battlelog, the web app for the Battlefield games, is load tested using Locust, so one can really say Locust is Battle tested ;).
Need Dedicated Support?
Locust.cloud provides dedicated commercial support for Locust.

I'm impressed not more people talk about locust (http://locust.io/). The thing is awesome :) Shoutout too the guys from ESN :)
Armin Ronacher @mitsuhiko Author of Flask, Jinja2 & more

it’s become a mandatory part of the development of any large scale HTTP service built at DICE at this point.
Joakim Bodin @jbripley Lead Software Engineer at EA/DICE

locust.io is pretty fantastic, wish it had a bit more in the way of docs for non-HTTP stuff though
Alex Gaynor @alex_gaynor Django & PyPy core developer

locustfile.py

from locust import HttpUser, between, task


class WebsiteUser(HttpUser):
    wait_time = between(5, 15)
    
    def on_start(self):
        self.client.post("/login", {
            "username": "test_user",
            "password": ""
        })
    
    @task
    def index(self):
        self.client.get("/")
        self.client.get("/static/assets.js")
        
    @task
    def about(self):
        self.client.get("/about/")

# This locust test script example will simulate a user 
# browsing the Locust documentation on https://docs.locust.io

import random
from locust import HttpUser, between, task
from pyquery import PyQuery


class AwesomeUser(HttpUser):
    host = "https://docs.locust.io/en/latest/"
    
    # we assume someone who is browsing the Locust docs, 
    # generally has a quite long waiting time (between 
    # 10 and 600 seconds), since there's a bunch of text 
    # on each page
    wait_time = between(10, 600)
    
    def on_start(self):
        # start by waiting so that the simulated users 
        # won't all arrive at the same time
        self.wait()
        # assume all users arrive at the index page
        self.index_page()
        self.urls_on_current_page = self.toc_urls
    
    @task(10)
    def index_page(self):
        r = self.client.get("")
        pq = PyQuery(r.content)
        link_elements = pq(".toctree-wrapper a.internal")
        self.toc_urls = [
            l.attrib["href"] for l in link_elements
        ]
    
    @task(50)
    def load_page(self):
        url = random.choice(self.toc_urls)
        r = self.client.get(url)
        pq = PyQuery(r.content)
        link_elements = pq("a.internal")
        self.urls_on_current_page = [
            l.attrib["href"] for l in link_elements
        ]
    
    @task(30)
    def load_sub_page(self):
        url = random.choice(self.urls_on_current_page)
        r = self.client.get(url)

# An example on how to use and nest TaskSets

from locust import HttpUser, TaskSet, task, between

class ForumThread(TaskSet):
    pass

class ForumPage(TaskSet):
    # wait_time can be overridden for individual TaskSets
    wait_time = between(10, 300)
    
    # TaskSets can be nested multiple levels
    tasks = {
        ForumThread:3
    }
    
    @task(3)
    def forum_index(self):
        pass
    
    @task(1)
    def stop(self):
        self.interrupt()

class AboutPage(TaskSet):
    pass

class WebsiteUser(HttpUser):
    wait_time = between(5, 15)
    
    # We can specify sub TaskSets using the tasks dict
    tasks = {
        ForumPage: 20,
        AboutPage: 10,
    }
    
    # We can use the @task decorator as well as the  
    # tasks dict in the same Locust/TaskSet
    @task(10)
    def index(self):
        pass