How to Set HTTP Request Headers in Locust

In Locust, configuring HTTP request headers is straightforward by passing a headers dictionary to the client methods.

1. Basic GET request with custom headers

from locust import HttpUser, task, between

class WebsiteUser(HttpUser):
    wait_time = between(1, 5)  # set user wait time

    @task
    def get_with_custom_header(self):
        headers = {
            'Authorization': 'Bearer your_access_token',
            'Content-Type': 'application/json'
        }
        self.client.get("/api/resource", headers=headers)

This example defines a WebsiteUser class that inherits from HttpUser ; the get_with_custom_header task creates a header dictionary with an authorization token and JSON content type, then sends a GET request.

2. POST request with custom headers and JSON payload

@task
def post_with_custom_header(self):
    headers = {
        'Authorization': 'Bearer your_access_token',
        'Content-Type': 'application/json'
    }
    payload = {
        "title": "foo",
        "body": "bar",
        "userId": 1
    }
    self.client.post("/api/resource", json=payload, headers=headers)

Here the same headers are used for a POST request, and a JSON payload is supplied via the json argument.

3. Sharing headers across multiple requests

from locust import HttpUser, task, between

class WebsiteUser(HttpUser):
    wait_time = between(1, 5)

    def on_start(self):
        """Called when a virtual user starts"""
        self.headers = {
            'Authorization': 'Bearer your_access_token',
            'Content-Type': 'application/json'
        }

    @task
    def make_requests(self):
        self.client.get("/api/resource1", headers=self.headers)
        self.client.post("/api/resource2", json={"key": "value"}, headers=self.headers)

By defining self.headers in the on_start method, the same header set can be reused for any subsequent requests, avoiding repetition.

Notes

• Security: Do not hard‑code sensitive information such as API keys; use environment variables or external configuration files.

• Dynamic updates: If header values change during a test, ensure they are refreshed before each request.

• Error handling: Incorporate appropriate error handling to manage network failures or unexpected server responses.