Is HTML validation necessary for ranking?
Why Webmasters Stack Exchange recommends it
Webmasters Stack Exchange answerers point people to it as Google's own statement that HTML validation errors do not hurt SEO as long as the page still renders properly.
Recommended by 2 people across 2 different months, 2011 to 2016.
What it is
A short Google Webmaster Help video in which Matt Cutts, joined by a guest, answers a viewer question about whether valid HTML is needed for search ranking. The answer is that validation itself is not a ranking factor, though pages that render broken for users are a separate concern.
What people said
Recommends Paolo · 2012-02 · Webmasters Stack Exchange · on “Does valid HTML, CSS and/or XML affect SEO?”
If no information is lost and the rendering is not badly broken, valid HTML is not that important for ranking/SEO. Watch this video from Google Webmasters Help for a better explanation: Is HTML validation necessary for ranking? [this video]
Recommends Goyllo · 2016-04 · Webmasters Stack Exchange · on “Is using the <u> tag invalid or bad for SEO?”
Using <u> tag in any webpage does not affect in SEO. If I was there then I will check How Google view my page or render my page, you can check that on Google search console. Here is two [this video] videos [LINK] from matt cutts about HTML validation.
Cites Su' · 2011-10 · Webmasters Stack Exchange · on “W3C Compliance v SEO”
@JohnConde Is HTML validation necessary for ranking? [this video] from mid-March 2011 still basically says no. Osvaldo, unless you can back up the validation comment better, I'd remove it. (Though I do still think the question should be closed as a dupe.)
Cites Stephen Ostermiller · 2013-09 · Webmasters Stack Exchange · on “How to mark up a poem in HTML for SEO”
The structure of your markup usually has no impact on search engines. For example, Google has said that they don't even care whether or not your markup "validates", as long as it doesn't look broken to users: [this video] There is only one time when specific markup helps: when search engines display listings differently in the result pages because semantic markup [LINK] exists in the page. The semantic markup suggested by John Conde is fine, but it will have no impact on your rankings or your display in the results because Google doesn't (currently) have a special display format for poems.
Cites Stephen Ostermiller · 2013-11 · Webmasters Stack Exchange · on “Cannot solve errors on W3C validator”
Solving validation errors in your site's HTML code will NOT help your rankings in search engines. Here is a video where Matt Cutts weights in on the situation [this video] : Matt : Hi. We have a guest to answer today’s webmaster video question. The question comes from Jimmy @Feldon, Wirsberg. Nice job getting your Twitter handle in there by the way. Jimmy asks, “Hi Matt. In a previous video, you stated that validation of HTML wasn't really important for ranking or SEO. This confuses me. Wouldn't Google really want to send its users to websites which would be broken for a lot of them?” Danny, how would you answer that? Danny : Well, a lot of websites can have invalid code but actually render just