Warning: This document is for an old version of Rasa. The latest version is 1.2.3.


Actions are the things your bot runs in response to user input. There are three kinds of actions in Rasa Core:

  1. Default actions: action_listen, action_back, action_restart, action_default_fallback
  2. Utterance actions: start with utter_, just send a message to the user
  3. Custom actions: any other action, these actions can run arbitrary code

Utterance Actions

To define an utterance action (ActionUtterTemplate), add an utterance template to the domain file that starts with utter_:

    - "this is what I want my action to say!"

It is conventional to start the name of an utterance action with utter_. If this prefix is missing, you can still use the template in your custom actions, but the template can not be directly predicted as its own action. See Responses for more details.

If you use an external NLG service, you don’t need to specify the templates in the domain, but you still need to add the utterance names to the actions list of the domain.

Custom Actions

An action can run any code you want. Custom actions can turn on the lights, add an event to a calendar, check a user’s bank balance, or anything else you can imagine.

Core will call an endpoint you can specify, when a custom action is predicted. This endpoint should be a webserver that reacts to this call, runs the code and optionally returns information to modify the dialogue state.

To specify, your action server use the endpoints.yml:

  url: "http://localhost:5055/webhook"

And pass it to the scripts using --endpoints endpoints.yml.

You can create an action server in node.js, .NET, java, or any other language and define your actions there - but we provide a small python SDK to make development there even easier.

Custom Actions Written in Python

For actions written in python, we have a convenient SDK which starts this action server for you.

The only thing your action server needs to install is rasa-sdk:

pip install rasa-sdk


You do not need to install rasa for your action server. E.g. it is recommended to run Rasa in a docker container and create a separate container for your action server. In this separate container, you only need to install rasa-sdk.

If your actions are defined in a file called actions.py, run this command:

python -m rasa_sdk --actions actions

In a restaurant bot, if the user says “show me a Mexican restaurant”, your bot could execute the action ActionCheckRestaurants, which might look like this:

from rasa_sdk import Action
from rasa_sdk.events import SlotSet

class ActionCheckRestaurants(Action):
   def name(self):
      # type: () -> Text
      return "action_check_restaurants"

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

      cuisine = tracker.get_slot('cuisine')
      q = "select * from restaurants where cuisine='{0}' limit 1".format(cuisine)
      result = db.query(q)

      return [SlotSet("matches", result if result is not None else [])]

You should add the the action name action_check_restaurants to the actions in your domain file. The action’s run method receives three arguments. You can access the values of slots and the latest message sent by the user using the tracker object, and you can send messages back to the user with the dispatcher object, by calling dispatcher.utter_template, dispatcher.utter_message, or any other rasa_sdk.executor.CollectingDispatcher method.

Details of the run() method:

Action.run(dispatcher, tracker, domain)

Execute the side effects of this action.

  • dispatcher (CollectingDispatcher) – the dispatcher which is used to send messages back to the user. Use dipatcher.utter_message() or any other rasa_sdk.executor.CollectingDispatcher method.
  • tracker (Tracker) – the state tracker for the current user. You can access slot values using tracker.get_slot(slot_name), the most recent user message is tracker.latest_message.text and any other rasa_sdk.Tracker property.
  • domain (Dict[Text, Any]) – the bot’s domain

A dictionary of

rasa_sdk.events.Event instances that is returned through the endpoint

Return type:

List[Dict[Text, Any]]

There is an example of a SlotSet event above, and a full list of possible events in Events.

Default Actions

There are three default actions:

action_listen stop predicting more actions and wait for user input
action_restart reset the whole conversation, usually triggered by using /restart
action_default_fallback undoes the last user message (as if the user did not send it) and utters a message that the bot did not understand. See Fallback Actions.

All the default actions can be overwritten. To do so, add the action name to the list of actions in your domain:

- action_listen

Rasa Core will then call your action endpoint and treat it as every other custom action.

Execute Actions in Other Code

Rasa Core will send an HTTP POST request to your server containing information on which action to run. Furthermore, this request will contain all information about the conversation.

As a response to the action call from Core, you can modify the tracker, e.g. by setting slots and send responses back to the user. All of the modifications are done using events. There is a list of all possible event types in Events.