How important is W3C validation for SEO?

I don't think it is very important. I checked some of the popular websites and their W3C code (or whatever it's called) contains many errors and warnings.
It's the world wide web consortium which was founded in MIT. Their goal is to write standards and protocols like HTML and XML in order to make the web more organized and help it grow the best. I don't see a significant connection to SEO. However, the biggest and best built sites are usually validated.
Websites should be free from obvious errors, but its possible to fail validation without any obvious errors. Fix the type of errors that prevent the spider from crawling the site. Fix the obvious errors and don't sweat the small errors.
Nowadays it doesn't matter that much. You should worry about structured data and now ;)
There is one place where it matters quite a bit. If you fail to close a statement, it can cause whole sections of your site to not be readable, or to be included into a weighted section of the algorithm.

If like a lot of people you use the h tags to control font size, and forget to close the statement all the text to the next h tag will be considered as tag content and the appropriate weight applied to the words.

It can also affect styling for those words, making them appear differently on different browsers..

If you fail to close a comment, the page will ignore everything until the end of the next comment statement. This can cause things to disappear that you might not notice, or properties to be inhertied that you cannot figure out.

The major browsers are very good at displaying screwed up code correctly by making guesses as to the intent of the coder, but other platforms are much more likely to have these problems that actually affect the site display.

Even when the browser makes a guess, that is what it is, a guess. It may or may not be what you had in mind.

Lastly, if you at least TRY to validate your code, you will learn how to code better.

Just because the page is displaying properly does not mean that the content of the page is correctly understood.

THAT can affect rankings.
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Hey shahid,
it is sweat the small errors it doesn't matter that much. You should worry about structured data
Actually, W3C is factured into G's algo. Simply because a well code site raises it's trust factor, allows bots to flow easier, and is presumed to hold a greater/better user experience. However, load speed is much more important than compliance. Your goal should always be to get your site under 1 second load time. You can test your site at
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