# Designing validation for existing apps > To enhance the user experience and productivity, you can use the Trigger-based Attended Automation solution to design custom validation for existing applications. This tutorial demonstrates how to design validations using callouts, forms, and triggers, for a smooth user experience while using the **UiDouble** sample application. To enhance the user experience and productivity, you can use the Trigger-based Attended Automation solution to design custom validation for existing applications. This tutorial demonstrates how to design validations using callouts, forms, and triggers, for a smooth user experience while using the **UiDouble** sample application. The steps below show an overview on how to create validation for the **UiDouble** application: 1. Create a callout with only a **Label/Header** component, meant to display the validation message at runtime (**callout.uiform**). 2. Create a general workflow that validates the value typed in the **On Cash In** and **On Us Check** UI elements (**validate.xaml**). Whenever the validation condition is broken (in this example, `elDouble > minValue`), a callout with the appropriate message (for example, `text`) shows. 3. Create a trigger workflow to validate the data inside the **On Us Check** field. It should contain an [Application Event Trigger](https://docs.uipath.com/activities/other/latest/user-guide/n-native-event-trigger) activity and an **Invoke Workflow File** activity. This means that when the user adds data into the field, the **validate.xaml** file is invoked to perform validation (**on us check changed.xaml**). 4. Create a trigger workflow to validate the data inside the **Cash In** field. It should contain an **Application Event Trigger** activity and an **Invoke Workflow File** activity. This means that when the user adds data into the field, the **validate.xaml** file is invoked to perform validation (**on cash in changed.xaml**). 5. Create another trigger workflow that validates both fields, when user clicks **Accept**. You can achieve this using an **Application Event Trigger** activity. If both fields are valid, then you can replay the user event that clicked the **Accept** button (**on accept clicked.xaml**). ## Sample project Learn how to create validation for the **UiDouble** app, using [this sample project](https://documentationexamplerepo.blob.core.windows.net/examples/TriggerBasedAttendedAutomation/Custom_Validation_Tutorial.zip) as inspiration. You can download the **UIDouble** application [here](https://documentationexamplerepo.blob.core.windows.net/examples/TriggerBasedAttendedAutomation/UIDouble.exe). ## Video example Check out the video below, that walks you through designing the sample project and then testing it.