Web Validation (W3C Validation): How, When and Why

Published by

Anna Abram activities: SEO Expert

Oct 27, 2021

It is known as a website validating to the process during which it is verified that all the pages that compose it obtain satisfactory results in a series of tests to which they will be subjected. These tests are carried out by validation tools developed according to standards and ensure that a file of a specific language (such as HTML) complies with certain criteria. The body that regulates these standards is the W3C (a distorted name is wc3 validation) (World Wide Web Consortium), an international consortium that makes recommendations for the operation of the Internet.


It should be clarified that web pages can work even when they do not comply with these standards and therefore do not pass the validation. Since this is not a requirement, not all pages are validated, and in fact, many developers do not spend their time doing so.


As we all know, HTML is not a programming language but for the representation and communication of information. For this reason, it is not compiled but is interpreted by special programs that we call browsers (although Microsoft tried to call them explorers). The point is that this fact of being interpreted and not compiled gives it one of its main advantages and disadvantages:


On the positive side, a page doesn't need to be perfectly written to be interpreted. An error will not cause the page not to load, but in the worst case, it will make an area look bad, or it may even go unnoticed because our browser ignores it.


On the negative side, this freedom for browsers to ignore or interpret specific fields has led to each wanting to change the language to their liking. A page often varies depending on the browser used to display it.

The Why of Validation

With these premises, it seems easy to find out the need for validation. If we can strictly implement the World Wide Web Consortium (W3C) guidelines on language, we will have done everything in our power to make the page look good anywhere. And it will be the responsibility of each browser to display it following what is established in the language standards.

In that sense, by the mere fact of doing our job well, we may be interested in our documents complying with the format they claim to have. That is why our document must always begin by indicating the definition of the DOCTYPE.

But beyond our requirement, certain types of clients or situations require us to be more strict when you work on Website Development:


  • When you want compatibility with mobile devices.

  • When the page needs to be viewable in older browsers.

  • When the client belongs to a public administration.

  • When the page is going to show medical content or being visited by people with disabilities etc.


But be careful; the fact that our website complies with the W3C requirements does not imply quality results. It only assures us that, with minor exceptions, it will look equally good or equally bad in all browsers.


Tools to Validate Our Website

We are going to show you three tools that you can use to validate your WordPress site:


W3C Markup Validation Service: We need to enter our URL address in the box that we will find on your website and hit the "Check" button. A process will begin that will return a report with the errors found, modifications to the structure and others, about our HTML code of all the pages.


W3C Validation CSS Service: It is a tool very similar to the previous one, but with the difference that it is explicitly directed to CSS files. There we must enter the address of the CSS file and then click on the "Check" button. It will also return the analysis result, showing errors found or failing that, and it will tell us that everything is fine.


W3C Feed Validation Service: Similar to the previous tool, this one is oriented to the analysis of RSS feeds. In it, we will enter the feed's address, give "Check", and perform the test of our feed with the same results that we mentioned before. Generally, the address of our feed is "domain / feed".


It is essential to clarify that whenever we use WordPress themes, they must be from reputable developers. Indeed we will not have problems with validation since everything is well developed and ready to use. With other issues, however, we will not have that certainty.


How to Validate the Code

Ok, we have already understood why we want to validate, and we have reached that final stage where we have the time and resources to do so. Where to start?


As we said before, it will be essential to define the DOCTYPE that our code will respect since an HTML that is perfectly valid from the point of view of XHTML 1.1 will probably present many errors if we validate it against HTML 4.01 Strict, for example.


Our advice is that if you use XML, opt for XHTML 1.0 Transitional, which has characteristics common to XML. Such as all tags that do not have different opening and closing tags must include the slash / before finalizing. If not, HTML 4.01 Transitional should be enough for you.


As for using a Transitional definition instead of Strict, as the name itself says, the former is a transition model between what was state of the art before approving that version of HTML and the strict one. Actually, the Transitional usually includes duplicates that are no longer accepted in the Strict, such as:


<script language="JavaScript" type="text/javascript">



That tag opening script would be valid in Transitional but no longer in Strict, where its language disappears for the benefit of a single attribute type.


Whatever the DOCTYPE chose, or even for our CSS sheets or SVG images, the tool to use is the W3C validator. Entering our URL (or the bareback code, if the page is not yet open to the public) will warn us of the number of errors that prevent our code from being valid and warnings about details that we should improve.


In addition, the validator itself tells us in which line each error occurs, so the process is usually based on achieving minor corrections and going through the validator again.


Once the result is positive, the validator itself will urge us to use the corresponding icons to show that our page is valid.


We can go further and look for more tools that help us understand the impediments that our pages may present for certain groups of users.


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