I will lay down some facts on Google supplemental index which is based on days of research and actual experiments.Those of you who are worried about the repercussions if your website has supplemental index need not despair,This has nothing to do with any sort of penalty by Google
What exactly is the Google supplemental index?
Google indexes around 3.3 billion web pages and that’s a something huge. The search engine giant has set some parameters on the basis of which pages are crawled and indexed. Now Google has 2 web indexes, one is the main index and the other is the supplemental index. When for some reason Google feels that a particular page cannot be included in the main index, it puts it in the Supplementary Pages.
So are the pages in the supplemental index penalized by Google?
A big NO! Supplemental index is not an index of penalized pages, nor is a trash bin. As the search engine has to index billions of pages, they have set some quality parameters on the basis of which they include pages in the main or in the supplemental index. Many new pages go supplemental just for the reason that they don’t qualify enough to be in the main index.
What are the reasons for supplementary pages?
There are quite a few reasons for pages going supplemental. Those are:
Duplicate Content: This is one of the main reasons for supplemental pages. If pages share the same content, then one of those pages will surely make it to the supplemental index. The page which will be in the main index depends on some factors like page rank, backward links etc.
Same page Title and Description: If there are pages that have the same title and description, then many of those pages have a high chance of going supplemental. So it is always advised to keep page titles and description unique.
Canonical Issues: If there are 2 versions of the same page, one with WWW and another without WWW then one of those pages will go supplemental. It’s better to solve any such canonical issues with a 301 redirect to avoid pages going supplemental.
Lack of content: Give the spiders something to chew on. If a page has only images and lacks content, then most likely it will go supplemental. So you need to have a good combination of text and images on your pages to avoid the supplemental index.
Lack of Page Rank: This is also one of the factors that lead a page to the supplemental index.
Orphan Pages: If there are pages that are lying orphan, which means that the pages are not linked with the rest of your site, then the pages will so supplemental. So you should have a clear navigation in your site and make sure than none of your pages lie abandoned.
Dynamic URLs: If there are too many parameters in an URL then the page has a high chance of going supplemental. Dynamic pages are never preferred by the search engines, even though Google can index those pages. It’s best to rewrite those dynamic URLs into static ones. They are far more search engine friendly than dynamic ones.
Even after all these, pages can still go supplemental for some reasons that are known only to Google. But these reasons are the most common ones for supplemental pages.
You don’t need to be afraid of your supplemental pages. Use solid white-hat techniques for optimizing your site and build your site for your visitors, not for the search engines. Voluntarily link out to some related authority sites on your topic, this will help to increase your site’s trust rank and overall quality score. Sites having higher Trust Rank and quality score seem to avoid the supplemental index much easily.
At the end, I’d like to mention that even the personal site of Matt Cutts, head of Google web-spam team has some of its pages in the supplemental index and so are pages of Yahoo and MSN. So there’s not much to worry, Google will pull out your pages of the supplemental index once it finds those pages worthy enough to be in the main index. So have great content and build links from quality and related sites.