What are Google Supplemental Results?

SEO Question: Much of my website is in Google's Supplemental index? What is their supplemental index? How does it work?

SEO Answer: What a timely question...where to start...well if the supplemental problem has only hit your site recently (as compared to the date of this post) it may be a Google specific problem that has caused them to dump thousands of sites recently.

Believe it or not, other than the home page most of this site is currently in supplemental results as of typing this, and with the current Google hole you can throw sites into supplemental hell within 72 hours.

Matt Cutts, a well known Google engineer, recently asked for feedback on the widespread supplemental indexing issue in this thread. As noted by Barry, in comment 195 Matt said:

Based on the specifics everyone has sent (thank you, by the way), I'm pretty sure what the issue is. I'll check with the crawl/indexing team to be sure though. Folks don't need to send any more emails unless they really want to. It may take a week or so to sort this out and be sure, but I do expect these pages to come back to the main index.

In this thread SEM4U points out that 72.14.207.104 was showing fewer supplemental sites than he saw on others like 64.233.179.104.

Some people are conspiring that generally lots of listed pages were dropped and only the longstanding supplemental pages remain, but that theory is garbage on my site...since I still see a strong PageRank 6 Supplemental page that was recently ranking in the SERPs for competitive phrases (prior to going supplemental) that recently went supplemental.

I have done a site redesign just after this supplemental deal occured, but that was sorta in coincidence with this happening. One good thing about that MovableType update is that the last version of MovableType I was using created these aweful nuclear waste redirect pages...it don't do that on version 3.2.

As far as other reasons this site could have possibly been hit supplemental:

• too much similar text on each page - but I do think it is common to have common sales elements on many pages of a site, so I doubt that is it
• redirect links - affiliate links via Clickbank and the direct affiliate program might have flagged some sort of trigger if Google was trying to work on 301 & 302 issues... but whatever they did I don't think they did it better ;)
• Google is a bit hosed right now

What are supplemental results?

Supplemental results usually only show up in the search index after the normal results. They are a way for Google to extend their search database while also preventing questionable pages from getting massive exposure.

How does a page go supplemental?

From my experiences pages have typically gone supplemental when they became isolated doorway type pages (lost their inbound link popularity) or if they are deemed to be duplicate content. For example, if Google indexes the www. version of your site and the non www. version of your site then likely most of one of those will be in supplemental results.

If you put a ton of DMOZ content and Wikipedia content on your site that sort of stuff may go supplemental as well. If too much of your site is considered to be useless or duplicate junk then Google may start trusting other portions of your site less.

Negative side effects of supplemental:
Since supplemental results are not trusted much and rarely rank they are not crawled often either. Since they are generally not trusted much and rarely crawled odds are pretty good that links from supplemental pages likely do not pull much - if any - weight in Google.

How to get out of Google Supplemental results?
If you were recently thrown into them the problem may be Google. You may just want to give it a wait, but also check to make sure you are not making errors like www vs non www, content manangement errors delivering the same content at multiple URLs (doing things like rotating product URLs), or too much duplicate content for other reasons (you may also want to check that nobody outside your domain is showing up in Google when you search for site:mysite.com and you can also look for duplicate content with Copyscape).

If you have pages that have been orphaned or if your site's authority has went down Google may not be crawling as deep through your site. If you have a section that needs more link popularity to get indexed don't be afraid to point link popularity at that section instead of trying to point more at the home page. If you add thousands and thousands of pages you may need more link popularity to get it all indexed.

After you solve the problem it still may take a while for many of the supplementals to go away. As long as the number of supplementals is not growing, your content is unique, and Google is ranking your site well across a broad set of keywords then supplementals are probably nothing big to worry about.