In ServiceNow, a UI Policy, Business Rule, and Client Script are tools used to control behavior and enforce logic on forms and records. A UI Policy runs on the client side and is used to dynamically show, hide, make fields mandatory, or read-only based on specific conditions without writing code. A Client Script also runs on the client side and allows you to write custom JavaScript to handle more complex logic on the form, such as autofilling fields, validating input, or reacting to field changes. In contrast, a Business Rule runs on the server side and is used to execute logic when records are created, updated, deleted, or queried—such as setting field values, sending notifications, or enforcing data integrity. These tools are often used together to ensure that both the user experience and the underlying data remain consistent and accurate.