locustio/locust · error · LocustError

No tasks defined. Use the @task decorator or set the 'tasks'

Error message

No tasks defined. Use the @task decorator or set the 'tasks' attribute of the SequentialTaskSet

What it means

SequentialTaskSet.get_next_task() cycles through self.tasks in order; if the tasks list is empty there is nothing to cycle, so it raises LocustError with guidance to define tasks via @task or the tasks attribute.

Source

Thrown at locust/user/sequential_taskset.py:63

class SequentialTaskSet(TaskSet, metaclass=SequentialTaskSetMeta):
    """
    Class defining a sequence of tasks that a User will execute.

    Works like TaskSet, but task weight is ignored, and all tasks are executed in order. Tasks can
    either be specified by setting the *tasks* attribute to a list of tasks, or by declaring tasks
    as methods using the @task decorator. The order of declaration decides the order of execution.

    It's possible to combine a task list in the *tasks* attribute, with some tasks declared using
    the @task decorator. The order of declaration is respected also in that case.
    """

    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self._task_cycle = cycle(self.tasks)

    def get_next_task(self):
        if not self.tasks:
            raise LocustError(
                "No tasks defined. Use the @task decorator or set the 'tasks' attribute of the SequentialTaskSet"
            )
        return next(self._task_cycle)

View on GitHub (pinned to f391a716e1)

Solutions

1. Add at least one @task decorated method to the SequentialTaskSet class
2. Or set the 'tasks' attribute to a non-empty list of task callables/classes
3. Verify the class you're running is the one with tasks defined (check inheritance and that tasks aren't filtered out by tags at runtime)

Example fix

// before
class MyFlow(SequentialTaskSet):
    pass
// after
class MyFlow(SequentialTaskSet):
    @task
    def step_one(self):
        self.client.get("/")

if not getattr(MyFlow, "tasks", None):
    raise RuntimeError("SequentialTaskSet has no tasks defined")

def has_tasks(cls) -> bool:
    return bool(getattr(cls, "tasks", None)) or any(hasattr(v, "locust_task_weight") for v in vars(cls).values())

try:
    flow = MyFlow(user)
except LocustError as e:
    if "No tasks defined" in str(e):
        logging.error(f"{type(flow).__name__} lacks tasks")
    raise

When it happens

Trigger: Instantiating a SequentialTaskSet subclass with no @task methods and no tasks attribute (or an empty list), then the runner calls get_next_task() when executing the user.

Common situations: Empty placeholder TaskSet classes; tasks defined only on a base class in a way Locust doesn't pick up; conditional task registration that ended up empty; typos like assigning 'task' instead of 'tasks'.

Related errors

• The 'tasks' attribute can only be set to list or dict
• No Markov tasks defined in class {classname}. Use the @trans
• In order to use a with-block for requests, you must also pas
• Tried to set status on a request that has not yet been made.
• If you want to change the state of the request using .succes

AI-assisted analysis of locustio/locust@f391a716e1 (2026-08-29). Data as JSON: /api/errors/99cb7e8bd91977d2. Report an issue: GitHub.