Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, for debugging an application are provided. In some aspects, a method includes detecting rendering of a digital component by an application executing on the device. A first signals indicative of visible attributes of content assets of the test digital component and second signals indicative of hierarchical associations between the content assets as rendered are obtained. A validation process the compares the first signals and the second signals to a set of requirements is invoked. A determination is made that one or more requirements are not met by the first signals or the second signals. In response to determining that the one or more requirements are not met a non-compliant overlay is provided within the application indicating that the digital component fails to comply with the one or more requirements.