Google's John Mueller said in a Google Hangout that it is better to have a website with valid HTML:
“This happened recently with the change of guidelines, in regards to the changes that were made to the webmaster guidelines. We mentioned 'use valid HTML'. The question here is: Is W3C validation (Broken HTML) ranking factor or should we give importance to that?
It is not directly a ranking factor. It doesn't mean that if your site is not using valid HTML we will remove it from the index. Because I think we're going to have a very empty list of search results.
However, there are some aspects that come into play. On the one hand, a site with really broken HTML, something we see very rarely, it is very difficult for us to crawl and index the content because we can't find it.
The other two aspects are more in regards to structured data. Sometimes it is very difficult to collect structured data when the HTML has been completely broken. Therefore you cannot easily use a validator for structured data.
The other factor is regarding the mobile devices and compatibility in browsers, if the HTML code has been broken, then it is sometimes very difficult to adapt on newer devices.”
This Tweet confirms a shorter statement John Mueller made the day before:
What does this mean exactly?
This means that there is no penalty for broken HTML code. Google can handle a lot of HTML errors. However, some HTML errors make it difficult for Google to index your web pages.
Some HTML errors can cause problems with structured data tags, other errors can cause display problems on mobile devices.
For that reason, it's much better to make sure your web pages use valid HTML. Valid HTML is a sign of a high-quality website.
Source: Free Seo News
