External links — outbound links — point from your site to another domain. They show the sources behind your claims, and where the relationship is special (ads, user submissions) the rel attribute communicates that to search engines.
External vs. Internal Links vs. Backlinks
The phrase 'external link' is used for both outbound and inbound links depending on context, which is a common source of confusion. This guide covers outbound links — the ones going from your site to someone else's.
External links (outbound)
Your site → another siteYou place them and you control them. The subject of this guide.
Internal links
Your site → your siteAffect how authority is distributed and how efficiently your site is crawled.
Backlinks (inbound)
Another site → your sitePlaced by someone else, so not directly under your control.
For links within your own site, see the internal linking guide, and for backlinks and site-level authority, the domain power guide.
Do External Links Leak SEO Value?
The idea that outbound links drain PageRank comes from PageRank sculpting — an old practice of deliberately hoarding link equity. Google no longer recommends it, and does not state that having outbound links is penalized in itself.
Equally, Google has not said that adding outbound links raises rankings. That distinction is worth keeping precise. The practical value lies not in ranking mechanics but in whether your article can show its evidence.
Our own SEO check uses three or more external links per page as a rough threshold. That is not an official Google criterion — it is our tool's heuristic for whether a page shows its sources.
Choosing the Right rel Attribute
Google's Search Central documentation describes nofollow, sponsored, and ugc as ways to qualify outbound links. The latter two were introduced in 2019, and since then these attributes have been treated as hints for ranking purposes.
rel="nofollow"
You cannot vouch for the destination
A source cited as an object of discussion, or a reference you have not fully vetted
rel="sponsored"
Compensation is involved — ads, sponsorships, affiliates
Destinations inside sponsored posts, affiliate links, paid banner placements
rel="ugc"
The link appears in user-contributed content
Links in comments, forum posts, and reviews
No attribute
You can stand behind the destination as a reference
Official documentation, primary sources, research data offered as evidence
Attributes can be combined. A user-submitted link that is also promotional can carry rel="ugc sponsored".
Outbound Links as Citations in the AI Era
The real job of an outbound link is to expose the basis of what you wrote. An article that shows whose research a number came from, or which official document a specification is based on, is verifiable in E-E-A-T terms.
The same applies when AI answers cite sources: attributed statements are easier material to work with. That said, no causal link between adding citations and being cited has been demonstrated. What can be said with confidence is that an assertion with no traceable basis is unverifiable to human readers too.
On measuring citation in AI search, see the AIO optimization guide.
Practical Rules for Outbound Links
Pair each claim with its source
Linking from the exact sentence that states a number beats a list of references at the end — both readers and search engines can follow the correspondence. Embed them naturally as 'according to …'.
Prefer primary sources
When several articles cover the same figure, link the original study or the official documentation rather than a roundup. Primary sources tend to keep their URLs through updates, so they break less often.
Name the source in the anchor text
Write 'Google Search Central's documentation on links' rather than 'here'. Readers can judge before clicking, and search engines understand what the destination is about.
Always qualify links involving compensation
Publishing ad, affiliate, or sponsored-post links without the sponsored attribute can run into Google's link spam policies. When in doubt, add the attribute.
Audit for broken links periodically
External links disappear at the other party's discretion. An article whose cited URL now 404s stays published with its evidence gone. Fold this into your content audits.
Common Mistakes
Avoiding citations out of fear of leaking authority
The result is an article that asserts numbers without showing where they came from. Google does not state that outbound links are penalized in themselves — unsupported assertions are the bigger quality problem.
Applying nofollow to every external link
A blanket nofollow policy labels even primary sources you would happily vouch for as links you cannot stand behind. The attributes exist to distinguish relationships, not to be applied uniformly.
Publishing affiliate links with no attribute
Links involving compensation that lack the sponsored attribute can run into link spam policies. On monetized sites this is the single item most worth double-checking.
Citing without opening the destination
Borrowing a number second-hand sometimes leads to a different figure at the original — or no original at all. If you present something as a source, open it and verify it yourself.
Good vs. Bad Implementations
<a href="https://roundup.example/…">here</a>
Second-hand link to a roundup, with anchor text that says nothing.
<a href="https://official.example/report">the ministry's annual usage survey</a>
Links the primary source, and names it in the anchor text.
<a href="https://af.example/xxx">recommended tool</a>
Compensation is involved but no attribute is present.
<a href="https://af.example/xxx" rel="sponsored">recommended tool</a>
The relationship is declared.
<a href="https://user.example/">a URL posted by a user</a>
Reads as though you vouch for the submitted content.
<a href="https://user.example/" rel="ugc nofollow">a URL posted by a user</a>
Signals that the link is user-generated.
