Sometimes you are so much engrossed in your code that you do not have time to nitpick minor details. You decide to live with those problems until the time when you can dig deeper and fix those issues. However, there are some issues that can be instantly fixed and make your code cleaner and compliant with the standards. If you are in such a situation, try Holmes.
Holmes is a simple and stand-alone diagnostic CSS stylesheet that you can use to highlight potentially invalid, inaccessible or erroneous HTML(5) markup.
Holmes can be useful not only to fix inconsistencies or missing attributes but also to make your code standardized on W3C HTML5 standards. The simple stylesheet uses color codes to highlight obvious issues in your code such as missing tags, Non W3C elements, poor attributes etc. Holmes can be very useful while reviewing and debugging a really old website.
Holmes works with almost all popular browsers.