An in-depth review of the product (app, website, web app, etc.) content to reveal errors, inconsistencies, defaults, and deficiencies. The diagnostics will check if content serves its purpose, aligns with business goals, help users attain their wants & goals and solve their problems, and is accessible to different users, etc.
The result will be a comprehensive list of problems that were identified, recommended solutions, and the impact that the solutions will have on the product and the user experience.