When you have a 404, regardless of whether it is a default 404 or a custom 404, Google doesn’t crawl the content of the 404 once it sees the response is a server 404.  Why is this important?  Many have been creating custom 404s for SEO specific reasons.

So if we see a 404, then we see a 404 and don’t look at the content.  We don’t look to see what is visible on your 404 pages, on your server error pages, we essentially assume that something that the user can look at and kind of deal with, we don’t follow the content on pages that return any of these error response codes.

So why did custom 404s become a SEO thing as opposed to a user thing?  While custom 404s are important from a user perspective – they help get lost visitors to your site on either the page they wanted to go to, or just to other pages on the site they feel are interesting.

What makes this interesting is that in the Google Quality Rater Guidelines, they ask raters to look at what is on the 404 page, whether it is useful, and to rate it accordingly.  And since the rater guidelines essentially are guidelines for what Google wants to see on a high quality site, the fact that Google is just seeing the 404 being served, but not crawling to see what is on that 404 means that the value of the 404 page, in Google’s eyes, isn’t as high as previously thought.

Here is what the Google Quality Rater Guidelines say about 404s:

Of course, worth reminding again, from a user experience perspective, high quality 404 pages ARE important since it can help lead those users who somehow end up on a 404 page to another page on the site, rather than clicking the back button.

And oftentimes, many sites that do create custom 404 experiences tend to be higher quality since they want to help their users.  And it is something that they ask their Quality Raters to look for – and rate – when they are doing their ratings.  But from a strictly SEO perspective, if your 404 page returns a 404, Google isn’t looking at what you have on that 404 page.

It is also worth noting that links to your 404s do not help a site – so linking to other pages on your site from a 404 page which might have links to it won’t help from a ranking benefit either.  Lastly, 404 errors themselves do not cause any kind of Google penalty, as Google has noted the majority of 404s aren’t the fault of the site owner.

Bottom line, keep creating custom 404s because they are good for the user… but the suspected SEO value isn’t there.