Web: Faulty HTML, JS, and CSS code, hurts your page Performance, Quality and Debugging.

HTML page is the core

Yes, it is the core of every web project. Therefore, it is very important to code your HTML page properly since it forms the foundation for everything else. Because it is the core of every web page, so without a solid foundation, the stuff you build upon it will easily break.

All web browsers are very forgiving and will often render a page correctly even if the HTML is slightly faulty, and your page finally will render, but you should get your attention for such behavior. I do, however, recommend that you make sure the HTML is coded properly, for a number of reasons:

• Performance
  Correct HTML code renders faster than incorrect HTML.
  
  How it comes? Okay let us see, if your code done properly, the browser will interpret the HTML in strict mode, in which it assumes that you know what you are doing. Incorrectly done, and it will switch to quirks mode, in which it is a lot more forgiving in its interpretation of the code.
  
  This means that you can get away with sloppy code, but since the browser has to guess what you mean, the page takes longer to render.
  
  
• Quality
  Naturally, you want to look professional, and you just don’t look good with HTML that doesn’t validate. Invalid code is the sign of a developer who doesn’t know what he’s doing.
  
  
• Debugging
  
  In addition, if you don’t have the HTML right, strange errors may occur in your CSS or JavaScript that are really hard to find.
  
  Both the CSS and a lot of the JavaScript code relies on the HTML being correct, so to make it easier for yourself, make sure that your HTML is correct by validating it frequently.
  
  This will save you a lot of time and grief.
  
  

How do you know that you have a correct HTML code?

It is a simple answer, fortunately W3C (World Wide Web Consortium) provides a tool which validate your code, whether it is a live page by providing its URL, or resides on your computer by uploading the file or past the code.

You will find this validator at W3C markup validation service.

Also your browsers are bundled with validation and inspection tools such as developer tools, alongside a bunch of extensions you can add to your browser for validation process.

Some of Firefox browser tools:

1. Page Validator: https://addons.mozilla.org/en-US/firefox/addon/2250
2. Html Validator: https://addons.mozilla.org/en-US/firefox/addon/249
3. Web Developer Toolbar: https://addons.mozilla.org/en-US/firefox/addon/60

With these tools at your disposal, you are more than ready to get started.