# How automations work

An automation is a rule that lives on one field, the field whose change starts it. When that field changes on an item, or on one of an item's direct child items, the rule checks its conditions. If they hold, it sets or clears fields.

A rule runs as part of the change that starts it. Nothing checks it again later.

## When a rule runs

- **this item**: the field changed on the item. The rule tests and changes that item, and can also change its direct child items.
- **a child item**: the field changed on one of the item's direct child items. The rule runs on the parent, so **This item** in its conditions and actions means the parent.

A rule has one field that starts it. "When Priority is High and Finish is empty" lives on Priority or on Finish, and runs only when that field changes. To react to both, add a rule to each.

Some fields cannot start a rule: formulas, values shown from a parent, costs and tracked time. A formula, a parent's value or a cost is worked out, not saved, so it never changes on its own.

## What a change sets off

A field a rule sets on the item can start that field's own rules. Each rule runs at most once per change, so two rules cannot keep starting each other.

Fields a rule changes on child items do not start the child items' own rules.

## Example

Most organizations start with a rule on **Completed**: when a child item changes and every child item is completed, the parent is marked completed. Ticking the last open task in a project completes the project. That can start the project's own rules on **Completed** in turn.

A second rule, which reopens the parent when a child is not completed, starts switched off.

## Things that may surprise you

- **Creating an item runs no rule.** Only a change to the rule's field does.
- **No child is true for an item with no child items.** A rule that needs "no child is completed" also runs on an item with no children.
- **Setting a people field replaces who is on it.** It does not add to them.
- **User who triggered is whoever made the change.** That can be a different person each time.
- **A rule Chat adds starts switched off.** So does one Chat changes. It runs only once someone switches it on.
- **Only a role with Manage fields & types can add, change, delete or switch rules on or off,** in the app or in Chat. By default, only administrators have it.

## Next

- [How do I make a field change automatically?](../../types-and-fields/automate-fields-with-rules/)
- [Ask in Chat](../../integrations/assistant/)