The Render Tree is the browser's runtime representation of what can actually be displayed and interacted with on a web page. It is built by combining the DOM, which provides the page structure, with the CSSOM, which provides styling information. Unlike the DOM, the Render Tree excludes elements that are not rendered, such as those with display: none, and includes only the information needed to paint the page and determine its layout.
For software testers, the Render Tree helps explain why an element may exist in the DOM but still be impossible to click or see. Factors such as visibility, layout, overlapping elements, and pointer-events affect whether an element can receive user interactions. Many automation failures that appear to be locator problems are actually caused by differences between the DOM and the Render Tree. Understanding the Render Tree helps testers diagnose issues related to visibility, clickability, layout shifts, and interaction.
