Lume CSS Selector is a free Chrome add-on that enhances the browser's DevTools by integrating a dedicated tab for building CSS selectors. This tool is particularly beneficial for developers and testers working with automation frameworks like Selenium and Cypress. By allowing users to click on element attributes such as classes, IDs, and data-attributes, it simplifies the creation of precise CSS selectors needed for test automation.

Key features include an interactive hierarchy tree that visually represents the document structure, a per-attribute match count to gauge selector specificity, and a live highlight function that visually indicates matching elements on the page. Additional functionalities such as Prev/Next navigation, an Only Visible filter, and a one-click copy to clipboard option streamline the workflow, making it an essential tool for efficient web testing.