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

# Starting Flows

> How flows are triggered by LLM command generators or NLU intents, and how NLU triggers and flow guards control when they start.

Flows can be triggered by one of the following Rasa components: the LLM-based Command Generator
([SearchReadyLLMCommandGenerator](/docs/reference/config/components/llm-command-generators#searchreadyllmcommandgenerator) or
[CompactLLMCommandGenerator](/docs/reference/config/components/llm-command-generators#compactllmcommandgenerator), or the
[NLUCommandAdapter](/docs/reference/config/components/nlu-command-adapter).

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](/docs/reference/config/components/llm-command-generators#command-reference) 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](/docs/reference/primitives/starting-flows#nlu-trigger)
defined for your flow.

[Flow guards](/docs/reference/primitives/starting-flows#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:

```yaml title="flows.yml" {4-5} theme={null}
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:

```yaml title="flows.yml" {4-7} theme={null}
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](/docs/reference/config/components/nlu-command-adapter).

<Warning>
  In order to actually use `nlu_trigger`, you need to add the
  [NLUCommandAdapter](/docs/reference/config/components/nlu-command-adapter) before the `LLMCommandGenerator` to
  your NLU pipeline in the config file.
</Warning>

## 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`.

```yaml title="flows.yml" {4} theme={null}
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](/docs/reference/primitives/conditions) after the `if` key is not met, the flow cannot be started. However, there
are some exceptions to this:

1. The flow is triggered through a [link](/docs/reference/primitives/flow-steps#link) step from another flow.
2. The flow is triggered through a [call](/docs/reference/primitives/flow-steps#call) step from another flow.
3. The flow has defined intents with an [NLU trigger](/docs/reference/primitives/starting-flows#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](/docs/reference/primitives/flow-steps#link)
or [call](/docs/reference/primitives/flow-steps#call) step, you can specify that by adding `if: False`.
For example:

```yaml title="flows.yml" {4} theme={null}
flows:
  feedback_form:
    description: A flow should only be linked to.
    if: False
    steps:
      - action: my_action
```


## Related topics

- [Business Logic with Flows](/docs/reference/primitives/flows.md)
- [Flow Policy](/docs/reference/config/policies/flow-policy.md)
- [How to Trigger Flows](/docs/studio/build/flow-building/trigger-flows.md)
- [Flow Steps](/docs/reference/primitives/flow-steps.md)
- [Patterns](/docs/reference/primitives/patterns.md)