Starting Flows - Rasa Documentation

Flows can be triggered by one of the following Rasa components: the LLM-based Command Generator (SearchReadyLLMCommandGenerator or CompactLLMCommandGenerator, or the NLUCommandAdapter. LLM-based Command Generators use the descriptions of each of your flows, the running conversation, and other context to decide when to start a flow. It’s important to write clear and distinct descriptions for each of your flows to help the LLM decide which flow to trigger, or to issue a clarify command if the user hasn’t provided enough information. The NLUCommandAdapter uses a predicted intent to start a flow. In order to trigger a flow via the NLUCommandAdapter you need to have an NLU trigger defined for your flow. Flow guards are conditions that have to be met before a flow can be started. Adding flow guards provides additional control over when flows are triggered.

NLU Trigger

The nlu_trigger field is optional. If present, it contains a list of intents that can start the flow. If you don’t want to use a confidence threshold, list the intent names:

flows.yml

flows:
  my_flow:
    description: "A flow triggered with <intent-name>"
    nlu_trigger:
      - intent: <intent-name>
    steps:
      - action: my_action

If you only want the flow to trigger if the confidence is above a threshold, use the following syntax:

flows.yml

flows:
  my_flow:
    description: "A flow triggered with <intent-name>"
    nlu_trigger:
      - intent:
          name: <intent-name>
          confidence_threshold: 0  # threshold value, optional
    steps:
      - action: my_action

Multiple Intents in NLU Trigger

You can list multiple intents for the nlu_trigger. If any of these intents is predicted, the flow will be started by the NLUCommandAdapter.

In order to actually use nlu_trigger, you need to add the NLUCommandAdapter before the LLMCommandGenerator to your NLU pipeline in the config file.

Preventing Flows from Starting

Flow Guards

Flow guards are specified by adding an additional if field to the flow definition. For example, the following flow for showing the user’s latest bill can only be triggered if the slots authenticated and email_verified are both true.

flows.yml

flows:
  show_latest_bill:
    description: A flow with a flow guard.
    if: slots.authenticated AND slots.email_verified
    steps:
      - action: my_action

If the condition after the if key is not met, the flow cannot be started. However, there are some exceptions to this:

The flow is triggered through a link step from another flow.
The flow is triggered through a call step from another flow.
The flow has defined intents with an NLU trigger. In this case, intent trigger messages, for example/initialize_conversation, can “force start” a flow for a targeted intent.

If you have a flow which should exclusively be started via a link or call step, you can specify that by adding if: False. For example:

flows.yml

flows:
  feedback_form:
    description: A flow should only be linked to.
    if: False
    steps:
      - action: my_action

​NLU Trigger

​Multiple Intents in NLU Trigger

​Preventing Flows from Starting

​Flow Guards

NLU Trigger

Multiple Intents in NLU Trigger

Preventing Flows from Starting

Flow Guards