My site is accessible from two domains (example.com and example.net). How do I let Google know that the two domains are the same site?

#redirect 

• Use a 301 redirect to direct traffic from the alternative domain (example.net) to your preferred domain (example.com). This tells Google that your pages have been permanently moved, and is the best way to ensure that Google can crawl and index your site correctly. If you're changing domains, read about some best practices for making the move.

I have [thousands/several/at least two] links to my site, but when I search on Google it says I have [zero/not that many] links. What gives?

#number-of-links 

• If you do a Google search using the link: operator (e.g. [link:www.example.com]), you will see a sampling of pages that link to your site. For a more complete list of pages that link to you, verify your site in Webmaster Tools and then click the Links tab to see the sites that link to you.

I don't want Google to crawl my site. What should I do?

#stop-crawling

• You can set up a robots.txt file to control access and block Googlebot.
• Note that if other people link to pages on your site, these URLs may still show up in our index, and your site may still appear in search results.

What do I do if Googlebot is using too much of my bandwidth?

#crawl-rate

• If you'd like Google to crawl your site less often, use the crawl rate tool in your Google Webmaster Tools account.

Uh oh, Google indexed and is showing some pages that I wanted to keep private!

#remove-urls

• Use the URL Removal Request Tool to remove pages from Google's index.

Does validating my site (with a tool such as the W3C validator) help my site's ranking in Google's search results pages?

#valid-code

• No, at least not directly.  However, to the extent that cleaning up your HTML makes your site more accessible to people with disabilities or folks accessing your pages on portable or other devices, it can improve the popularity of your site... increasing natural links to your site (which can help with your Google ranking), traffic, and so on.

I have a lot of new links pointing to my site, but my site's Toolbar PageRank has not changed in months.

#pagerank

• Don't worry :).  We actually recalculate PageRank quite frequently, but only push Toolbar PageRank updates occasionally.  This is our respectful hint for you to worry less about PageRank, which is but one of over 200 signals that can affect how your site is crawled, indexed and ranked.

I recently purchased a domain that was previously associated with a spammy web site. What can I do?

#new-domain

• Verify your site in Webmaster Tools, then request reconsideration of your site.  

I found spam in Google's search results. Where can I report it?

#report-spam

• Please submit spam reports to http://www.google.com/contact/spamreport.html.
• Or better yet -- if you have a Webmaster Tools account -- you can report spam directly to Google. On the Dashboard, click Report spam in our index.  Note that you don't need to have an XML Sitemap in order to create an account, and you can typically create a Webmaster Tools account in under two minutes.  Spam reports sent via Webmaster Tools carry more weight than reports via our unauthenticated (open) spam report page.

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Don't forget to visit http://www.google.com/webmasters for comprehensive documentation, tools, our official blog, and much more!