Quick startΒΆ

Below is a quick little example of a simple locustfile.py:

from locust import HttpLocust, TaskSet

def login(l):
    l.client.post("/login", {"username":"ellen_key", "password":"education"})

def index(l):

def profile(l):

class UserBehavior(TaskSet):
    tasks = {index:2, profile:1}

    def on_start(self):

class WebsiteUser(HttpLocust):
    task_set = UserBehavior

Here we define a number of locust tasks, which are normal Python callables that take one argument (a Locust class instance). These tasks are gathered under a TaskSet class in the task attribute. Then we have a HttpLocust class which represents a User, where we define how long a simulated user should wait between executing tasks, as well as what TaskSet class should define the user’s “behaviour”. TaskSets can be nested.

The HttpLocust class inherits from the Locust class, and it adds a client attribute which is an instance of :py:class:`HttpSession <locust.clients.HttpSession>, that can be used to make HTTP requests.

Another way we could declare tasks, which is usually more convenient, is to use the @task decorator. The following code is equivalent to the above:

from locust import HttpLocust, TaskSet, task

class UserBehavior(TaskSet):
    def on_start(self):
        """ on_start is called when a Locust start before any task is scheduled """

    def login(self):
        self.client.post("/login", {"username":"ellen_key", "password":"education"})

    def index(self):

    def profile(self):

class WebsiteUser(HttpLocust):
    task_set = UserBehavior

The Locust class (as well as HttpLocust, since it’s a subclass) also allows one to specify minimum and maximum wait time - per simulated user - between the execution of tasks (min_wait and max_wait) as well as other user behaviours.

To run Locust with the above locust file, if it was named locustfile.py, we could run (in the same directory as locustfile.py):


or if the locust file is located elsewhere we could run:

locust -f ../locust_files/my_locust_file.py

To run Locust distributed across multiple processes we would start a master process by specifying –master:

locust -f ../locust_files/my_locust_file.py --master

and then we would start an arbitrary number of slave processes:

locust -f ../locust_files/my_locust_file.py --slave

If we want to run locust distributed on multiple machines we would also have to specify the master host when starting the slaves (this is not needed when running locust distributed on a single machine, since the master host defaults to

locust -f ../locust_files/my_locust_file.py --slave --master-host=


To see all available options type

locust –help