What is Google's Supplemental index?
Supplemental index is Google’s index of web pages, which Google considers ‘unimportant’. Google will query its supplemental index if it fails to find good matches within its main web index. For obscure or unusual queries, you may see some results appear from its supplemental index. They'll be flagged as "Supplemental Result" in green text, next to the URL Google shows for the listing.
Unlike its main index, which is updated all the time, the supplemental index is usually updated once about every quarter. While Google expects to see a fresher and more frequently updated supplemental index in the coming quarters, they do not foresee it becoming as comprehensive or frequently updated as their main index.
Are pages in the supplemental index doomed for a slow death?
Web pages inserted in supplemental index would rarely show up for competitive keyword searches. If they show up at all, the results from Google’s main index would show up towards the top, followed by results from the supplemental index. If a website’s pages are placed in supplemental index, it is a good indication that Google may not be sending too much search traffic for those pages from its search result pages. A good way to check if one’s site pages are in the supplemental index is to run a search on Google – “site:www.yoursite.com” (without the quotes), and browse through all the result pages to spot any “Supplemental Result” tags.
Contrary to what some SEO experts feel, when a site’s pages have been placed in the supplemental index, it does NOT indicate that the site has been penalized, even though the effect is somewhat the same. Google claims that it does not move a site's pages from their main index to their supplemental index in response to any violations of their Webmaster Guidelines.
Why do sites get trapped in the supplemental index?
There are four prime known reasons why web pages get into Google’s supplemental index –
1. Poor link-backs to the page (shows the content is not worth linking to)
2. Zero or very low PageRank (this is a result of point 1 above)
3. Duplicate content (within the site or copied from other websites)
4. No Content (pages with very little or no content)
From Google’s point of view, in all four instances, the pages demonstrate little value addition to its searchers.
Once we know the prime causes for sites getting into Google’s supplemental index, it is not to too difficult to address the issue.
1. Remove duplicate content
If a website has multiple copies of web content with little or no content variation, then these pages are likely to be placed in the supplemental index. One needs to remove all instances of duplicate content (intentional of unintentional) from the site. Sometimes, the content duplication happens unintentionally. For example, if a site’s pages have migrated from ‘.htm’ to ‘.php’ or ‘.asp’ and the older pages continue to reside on the server, probably linked from some old sitemap, then this would result in exact same ‘duplicate’ content appearing in the site twice over. Webmasters need to be careful not only to prevent duplicate content from residing on the server, but also capture traffic coming to older pages through a ‘301 redirect’ to the new pages. If a site’s navigation and menu renders most of the text on the page, and only a few product pictures or text change in several inner pages, then Google could consider these pages to be duplicate content. A good remedy in this case would be to limit unnecessary text navigation duplication and make efforts to elaborate product description in text. This is likely to add more value to even the human visitors of the site.
Affiliate sites which pick up content from a single network to populate their sites are likely to get their site pages in the supplemental index. As per Google, such duplicate content pages residing on different domains add little additional value to their search audience. Adding unique informative content will not only differentiate a site from other affiliates, but would also offer better services to its visitors and in turn get rewarded by Google.
2. Improve incoming links to the pages in supplemental index
Getting lots of incoming links to inner pages of a website, (particularly for new websites), will help retain the site in Google’s main index or move the site from the supplemental index to the main index. Older sites having high PageRank (PR4+) with several inner pages enjoying PR2+ would rarely see their pages in the supplemental index. However, if one has added lots of new pages to a new / low-PR site, without getting significant number of incoming links to the new pages, then there is a bright chance that the new pages may end up in the supplemental index. While it is a good practice to constantly seek good quality incoming links to one’s website, thumb rule is to focus larger portion of link building efforts towards the freshly made pages.
Webmasters involved in site optimization and promotion realize how difficult it is to get rewarded by search engines. The last thing they need is further hurdles in an already uphill task. A poor SEO planning can get a site into the supplemental index and can render all SEO efforts useless. A well planned strategy to build unique content and get quality incoming links to each page can yield a good return on site promotional investment. Remember, as the saying goes – ‘Prevention is better than cure’; it is easier to stay out of Google’s supplemental index than to get out of it.
Note: On 31st of July 2007, Google has declared that it has stopped displaying supplemental result tag on the search engine result page. While Google claims that this is due to the narrowing gap between the supplemental data and their main index, many feel that the tag removal is due to mounting pressure on Google from the webmaster community. While Google may have stopped displaying the tag, it is possible that they might still be keeping the data separately to facilitate faster query results. In any case, the reasons listed in this article for getting into supplemental index and improving the same for better search ranking are still worth addressing.