1. Changes from one index to the next.
Each time we update our database of web page (about once a month), our index shifts: we find new sites, we lose some sites, and site rankings change. If your site was dropped from Google and you have not made major changes to it in the last month, we will likely pick it up again in our next index. It's possible your site was simply inaccessible when our robots tried to crawl it.
You may want to check and see if the number of other sites linking to your URL has decreased. This is the single biggest factor in determining what sites are indexed by Google, as we find most pages when our robots crawl the web and jump from page to page via hyperlinks. To find out who links to your site, use Google's link: tool.
It's also possible your rank decreased because other sites were found and assigned a higher rank. You can be assured that no one at Google has hand adjusted the results to boost the ranking of a site. Google's order of results is automatically determined by several factors, including our PageRank algorithm. Please check out our "Why Use Google" page for more information on how this works.
- Multiple indices
We update our index about every four weeks. If you happen to enter the same query repeatedly while we are in the process of posting the index at our various data centers around the country, it might seem like you are seeing inconsistent results from Google. What is actually happening is that you are seeing a result from an 'old' version of our index one time and a result from a 'new' version the next. Due to the size of our index, we can not simultaneously post a new index at all of our data centers, which may result in this behavior for a short period of time.
- Other reasons
If your page does not appear at all, here are some other possible explanations.
Your site may not have been reachable when we tried to crawl it because of network or hosting problems. When this happens, we retry multiple times, but if the site cannot be crawled, it will not be listed in our current index. If it was a transient problem, your site will likely show up in the next index, which will be completed in a few weeks.
A technical glitch on our side may have caused us to 'miss' your site. In crawling more than 3 billion pages every few weeks, our system experiences hiccups from time to time. Again, this is a transient problem, and your site will likely show up in the next index. Please be patient with us during this period, as we are not able to modify our index by hand to add sites missed in this way.
The contents of your page or the links pointing to your page changed significantly and you no longer have a sufficiently high PageRank, or your page had low PageRank to begin with and a small change caused you to be dropped from the Google index.
Your page was manually removed from our index, because it did not conform with the quality standards necessary to assign accurate PageRank. We will not comment on the individual reasons a page was removed and we do not offer an exhaustive list of practices that can cause removal. However, certain actions such as cloaking, writing text that can be seen by search engines but not by users, or setting up pages/links with the sole purpose of fooling search engines may result in permanent removal from our index. If you think your site may fall into this category, you might try 'cleaning up' the page and sending a re-inclusion request to help@google.com. We do not make any guarantees about if or when we will re-include your site.