Outbound links, also called external links, are links that point from a page to a different domain. Seen from the page they lead to, the same links are inbound links, or backlinks.
What are they used for?
Outbound links point to sources, studies, tools or partners. They let readers check a claim. Technically they differ from internal links only in that the source and the target are on different domains. Wikipedia notes that the line can blur, for example between independent blogs hosted on subdomains of one platform.
Google’s SEO link best practices say that using external links can help establish trustworthiness, for example by citing your sources.
Marking links with rel attributes
Google describes three values in the rel attribute for qualifying outbound links.
sponsoredfor ads and paid placementsugcfor links in user-generated content such as comments and forum postsnofollowfor links where Google should not associate your site with the target and the other values do not fit
You can combine values, for example rel="ugc nofollow". Google says it will generally not follow links with these attributes, although the target page can still be found through sitemaps or other sites.
A different attribute controls data sharing. With rel="noreferrer" the browser sends no referrer to the target page when a visitor clicks the link.
Example
<a href="https://example.org/study">Study by the institute</a>
<a href="https://shop.example.com/product" rel="sponsored">Product in the shop</a>
<a href="https://forum.example.net/profile" rel="ugc nofollow">Author profile</a>
The first link is an editorial reference. The second is marked as paid, and the third comes from a forum post.
Common mistakes
- Leaving paid links unmarked. For ads Google recommends
sponsoredover the oldernofollow(see buying links). - Never checking outbound links, so they lead to dead pages over time (see link rot).
Sources
- Qualify your outbound links to Google – Google Search Centraldevelopers.google.com
- SEO link best practices – Google Search Centraldevelopers.google.com
- rel=noreferrer – MDN Web Docsdeveloper.mozilla.org
- Internal and external links – Wikipedia (supplementary)en.wikipedia.org
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