Synthetic tests in modern web applications often face challenges due to frequent UI updates and changes. To address this, locators are used to uniquely identify elements across different design iterations. CSS and xPath selectors are two common methods for creating locators, with CSS being easier to learn and read but offering fewer advanced querying options, while xPath provides more flexibility but requires a higher learning curve. Datadog Synthetic Monitoring offers a self-healing locator system that automatically covers most use cases, but also allows for customization using testing templates and user-created locators to address specific edge cases or intentional test failures. By implementing locators in synthetic tests, developers can ensure their applications remain resilient to UI changes and rendering issues.