> ## Documentation Index
> Fetch the complete documentation index at: https://docs.usefused.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Scheduled tasks

> Schedule folder-discovered queued tasks with a strict UTC cron expression.

A cron declaration targets an existing root `@task`. It does not expose a new
model tool.

<CodeGroup>
  ```python tasks/build_report.py theme={null}
  from harnest.task import task


  @task(queue="reports", max_retries=3)
  async def build_report(account_id: str) -> dict:
      return {"account_id": account_id, "status": "ready"}
  ```

  ```python cron/daily_report.py theme={null}
  from harnest import Cron
  from tasks.build_report import build_report


  daily_report = Cron(
      "0 9 * * 1-5",
      task=build_report,
      arguments={"account_id": "acct_123"},
  )
  ```
</CodeGroup>

The export name must match `cron/<name>.py`. Arguments are JSON-safe,
signature-checked at compile time, and kept in Harnest's private payload store.

## Schedule contract

| Rule      | Supported value                                               |
| --------- | ------------------------------------------------------------- |
| Fields    | Minute, hour, day of month, month, day of week                |
| Timezone  | `UTC` only                                                    |
| Syntax    | `*`, ASCII numbers, comma lists, ascending ranges, `/step`    |
| Ownership | Long-lived `harnest serve` or `harnest-agent serve` processes |
| Replicas  | Shared PostgreSQL commits one periodic occurrence             |

Each occurrence uses the schedule identity and timestamp as its idempotency
key, then enters the same private task queue as `task.defer(...)`. Every effect
must still be idempotent because a worker can retry after failure.

<Note>
  `harnest run` never activates schedules. The application still needs
  `HARNEST_TASK_DATABASE_URL` or one unambiguous PostgreSQL store.
</Note>

See [Queued tasks](/harnest/build/queued-tasks) for task results, retries, and
starting a fresh agent session from scheduled work.