## Each of these actions have a default behavior
In order to overwrite this default behavior, write a [custom action](/content/docs/reference/primitives/custom-actions/index.html) whose `name()` method returns the same name as the default action:

```python
class ActionRestart(Action):

def name(self) -> Text:
      return "action_restart"

async def run(
      self, dispatcher, tracker: Tracker, domain: Dict[Text, Any]
  ) -> List[Dict[Text, Any]]:

# custom behavior

return [...]
```

Add this action to the actions section of your domain file so your assistant knows to use the custom definition instead of the default one:

```yaml
actions:
  - action_restart
```

## Action Definitions

### action_listen
This action is predicted to signal that the assistant should do nothing and wait for the next user input.

### action_restart
This action resets the whole conversation history, including any slots that were set during it.
It can be triggered by the user in a conversation by sending a "/restart" message, if the [RulePolicy](https://legacy-docs-oss.rasa.com/docs/rasa/policies#rule-policy) is included in the model configuration. If you define an `utter_restart` response in your domain, this will be sent to the user as well.

### action_session_start
This action starts a new conversation session, and is executed in the following situations:
- at the beginning of each new conversation
- after a user was inactive for a period defined by the `session_expiration_time` parameter in the domain's [session configuration](/content/docs/reference/config/domain/#session-configuration/index.html)
- when a user sends a "/session_start" message during a conversation

The action will reset the conversation tracker, but by default will not clear any slots that were set.

#### Customization
The default behavior of the session start action is to take all existing slots and to carry them over into the next session. To demonstrate how to override this:

```python
from typing import Any, Text, Dict, List
from rasa_sdk import Action, Tracker
from rasa_sdk.events import SlotSet, SessionStarted, ActionExecuted, EventType

class ActionSessionStart(Action):
    def name(self) -> Text:
        return "action_session_start"

@staticmethod
    def fetch_slots(tracker: Tracker) -> List[EventType]:
        slots = []
        for key in ("name", "phone_number"):
            value = tracker.get_slot(key)
            if value is not None:
                slots.append(SlotSet(key=key, value=value))
        return slots

async def run(
      self, dispatcher, tracker: Tracker, domain: Dict[Text, Any]
    ) -> List[Dict[Text, Any]]:
        events = [SessionStarted()]
        events.extend(self.fetch_slots(tracker))
        events.append(ActionExecuted("action_listen"))
        return events
```

### action_default_fallback
This action undoes the last user-bot interaction and sends the `utter_default` response if it is defined. It is triggered by low action prediction confidence, if you have this [fallback mechanism](https://legacy-docs-oss.rasa.com/docs/rasa/fallback-handoff/) enabled.

### action_run_slot_rejections
This action runs [slot validation](/content/docs/reference/primitives/flow-steps/#slot-validation/index.html) rules written directly in the flows yaml file.

### action_trigger_search
This action can be used to trigger the Enterprise Search Policy from any [flow](/content/docs/reference/primitives/flows/index.html), rule or story. It works by manipulating the dialogue stack frame.

### action_reset_routing
This action is needed for [Coexistence of NLU-based and CALM systems](/content/docs/pro/calm-with-nlu/migrating-from-nlu/index.html). It acts as a softer version of the default action `action_restart`:

### action_clean_stack
This action plays a crucial role in maintaining stack integrity following a bot update.

### action_cancel_flow
This action is designed to gracefully terminate an ongoing conversation flow, ensuring a clean and controlled interruption of the current flow.

### action_hangup
This action is meant to be used in Voice Conversations to hang up a call.

### action_repeat_bot_messages
Verbatim repeat the last bot message. It is currently used for [conversation repair](/content/docs/pro/customize/patterns/index.html) in [two patterns](/content/docs/reference/primitives/patterns/index.html).

### action_default_capabilities
This action generates a user-facing reply that lists the flows currently startable for the active conversation.