Question: I have multiple domains that are all related. Should I be cross-linking between them to boost each other’s signals, or should I avoid cross-linking entirely?
When we say “cross-linking” we’re usually referring to the act sending links back and forth between two or more websites, either habitually or as a static element on each website. Cross-linking is often seen as a type of search engine manipulation, but there are times when cross-linking can be a valid technique.
We know from Google that linking 20 domains or more together will often be seen as a cross-linking scheme. But anyone would likely see that 20 domains is excessive, especially if they are low quality sites. When it comes down to two or three sites, it’s a different ballgame. When properly used, cross-linking can be used to shift an audience from one related site to another, such as the way The Onion, The A.V. Club, ClickHole and Onion Studios all link together into a single network. This is unlikely to produce any negative results, either from a user experience standpoint or a search engine optimization standpoint.
Ask yourself why you want to cross-link your sites. If you’re trying to cross-link for the purposes of increased PageRank, it’s probably not altogether helpful to cross-link (though you might want to send users from a high authority site to a lower authority site that you’re currently boosting). After all, if you’re cross-linking between two sites that don’t have any PageRank to begin with, you’re netting to the same end result. But if you’re trying to cross-link to improve user experience, directing users to information that is truly helpful to them, that’s another situation entirely.
Answer: Cross-linking between sites sparingly and when relevant is not harmful. Cross-linking between a multitude of websites (20 or more) could be harmful. Use discretion, but don’t shy away from it entirely when it’s needed.