The number of sites linking in that Alexa reports is the number of websites in the Common Crawl that link to a given website.
Here are a few explanations for cases where you know of links pointing to your site that Alexa does not list:
- The link is new and has not been picked up by the Common Crawl yet. You can find out when the Common Crawl was last updated in their blog.
- We count the number of sites linking in, and not the number of pages. (Only one link from a given site is counted.)
- We update the number of sites linking in only once per month for all sites. (Although the links-in count for sites with Certified Site Metrics are updated daily.)
- We don’t count links from link farms or other similar search engine placement mechanisms, such as links that are obviously from link exchanges.
- We don’t count links that appear in search results on a major search engine (such as Google, Bing, etc.). We do count links from non-search URLs on search engines, for example plus.google.com.
The Alexa traffic rank is in no way related to Sites Linking In.