DiagnostiCSS is a free Chrome add-on developed by the clever guys from Flatstack. It is a diagnostic CSS stylesheet that helps visually detect potentially invalid, inaccessible, or erroneous HTML markup. With DiagnostiCSS, web developers can easily identify and fix common issues in their HTML code.

One of the main features of DiagnostiCSS is its ability to highlight inline styles and event attributes, making it easier to identify and remove unnecessary or redundant code. This helps improve the overall cleanliness and maintainability of the HTML markup.

In addition, DiagnostiCSS also identifies invalid links, ensuring that all links within the HTML code are functioning correctly. This is particularly useful for websites with a large number of links, as it saves developers time by automatically flagging any broken or incorrect links.

Another important feature of DiagnostiCSS is its ability to detect empty or deprecated elements. By visually highlighting these elements, developers can quickly identify and replace them with more appropriate alternatives. This helps ensure that the HTML markup is up-to-date and compliant with current web standards.

Lastly, DiagnostiCSS helps identify elements that are missing required attributes. This ensures that all necessary attributes are included, preventing potential accessibility issues and improving the overall quality of the HTML markup.

Overall, DiagnostiCSS is a valuable tool for web developers who want to ensure the integrity and quality of their HTML markup. With its intuitive visual highlighting and comprehensive problem detection, DiagnostiCSS makes it easier to identify and fix issues, leading to more accessible and error-free websites.