# Creating Cascading Tool Inputs

Cascading input settings are useful when the value of one input field determines which subsequent inputs are shown. This makes the input process more streamlined, user-friendly, and error-free. This guide will walk through how to create cascading inputs for your tools.

## Prerequisites
Please make sure you have the latest version of [Prompt flow for VS Code](https://marketplace.visualstudio.com/items?itemName=prompt-flow.prompt-flow) installed (v1.2.0+).


## Create a tool with cascading inputs
We'll build out an example tool to show how cascading inputs work. The `student_id` and `teacher_id` inputs will be controlled by the value selected for the `user_type` input. Here's how to configure this in the tool code and YAML.

1. Develop the tool function, following the [cascading inputs example](https://github.com/microsoft/promptflow/blob/main/examples/tools/tool-package-quickstart/my_tool_package/tools/tool_with_cascading_inputs.py). Key points:
    * Use the `@tool` decorator to mark the function as a tool.
    * Define `UserType` as an Enum class, as it accepts only a specific set of fixed values in this example.
    * Conditionally use inputs in the tool logic based on `user_type`.

```python
from enum import Enum

from promptflow import tool


class UserType(str, Enum):
    STUDENT = "student"
    TEACHER = "teacher"


@tool
def my_tool(user_type: Enum, student_id: str = "", teacher_id: str = "") -> str:
    """This is a dummy function to support cascading inputs.

    :param user_type: user type, student or teacher.
    :param student_id: student id.
    :param teacher_id: teacher id.
    :return: id of the user.
    If user_type is student, return student_id.
    If user_type is teacher, return teacher_id.
    """
    if user_type == UserType.STUDENT:
        return student_id
    elif user_type == UserType.TEACHER:
        return teacher_id
    else:
        raise Exception("Invalid user.")
```

2. Generate a starting YAML for your tool per the [tool package guide](create-and-use-tool-package.md), then update it to enable cascading:

    Add `enabled_by` and `enabled_by_value` to control visibility of dependent inputs. See the [example YAML](https://github.com/microsoft/promptflow/blob/main/examples/tools/tool-package-quickstart/my_tool_package/yamls/tool_with_cascading_inputs.yaml) for reference.

    * The `enabled_by` attribute specifies the input field, which must be an enum type, that controls the visibility of the dependent input field.

    * The `enabled_by_value` attribute defines the accepted enum values from the `enabled_by` field that will make this dependent input field visible.
    > Note: `enabled_by_value` takes a list, allowing multiple values to enable an input.

```yaml
my_tool_package.tools.tool_with_cascading_inputs.my_tool:
  function: my_tool
  inputs:
    user_type:
      type:
      - string
      enum:
        - student
        - teacher
    student_id:
      type:
      - string
      # This input is enabled by the input "user_type".
      enabled_by: user_type
      # This input is enabled when "user_type" is "student".
      enabled_by_value: [student]
    teacher_id:
      type:
        - string
      enabled_by: user_type
      enabled_by_value: [teacher]
  module: my_tool_package.tools.tool_with_cascading_inputs
  name: My Tool with Cascading Inputs
  description: This is my tool with cascading inputs
  type: python
```

## Use the tool in VS Code
Once you package and share your tool, you can use it in VS Code per the [tool package guide](create-and-use-tool-package.md). We have a [demo flow](https://github.com/microsoft/promptflow/tree/main/examples/tools/use-cases/cascading-inputs-tool-showcase) you can try.

Before selecting a `user_type`, the `student_id` and `teacher_id` inputs are hidden. Once you pick the `user_type`, the corresponding input appears.
![before_user_type_selected.png](../../media/how-to-guides/develop-a-tool/before_user_type_selected.png)
![after_user_type_selected_with_student.png](../../media/how-to-guides/develop-a-tool/after_user_type_selected_with_student.png)
![after_user_type_selected_with_teacher.png](../../media/how-to-guides/develop-a-tool/after_user_type_selected_with_teacher.png)



## FAQs
### How do I create multi-layer cascading inputs?
If you are dealing with multiple levels of cascading inputs, you can effectively manage the dependencies between them by using the `enabled_by` and `enabled_by_value` attributes. For example:
```yaml
my_tool_package.tools.tool_with_multi_layer_cascading_inputs.my_tool:
  function: my_tool
  inputs:
    event_type:
      type:
      - string
      enum:
        - corporate
        - private
    corporate_theme:
      type:
      - string
      # This input is enabled by the input "event_type".
      enabled_by: event_type
      # This input is enabled when "event_type" is "corporate".
      enabled_by_value: [corporate]
      enum:
        - seminar
        - team_building
    seminar_location:
      type:
      - string
      # This input is enabled by the input "corporate_theme".
      enabled_by: corporate_theme
      # This input is enabled when "corporate_theme" is "seminar".
      enabled_by_value: [seminar]
    private_theme:
      type:
        - string
      # This input is enabled by the input "event_type".
      enabled_by: event_type
      # This input is enabled when "event_type" is "private".
      enabled_by_value: [private]
  module: my_tool_package.tools.tool_with_multi_layer_cascading_inputs
  name: My Tool with Multi-Layer Cascading Inputs
  description: This is my tool with multi-layer cascading inputs
  type: python
```
Inputs will be enabled in a cascading way based on selections.