How Google detects paid links
Google has not published its method. What is known is that a machine learning system called SpamBrain looks for sites that buy links and sites that sell them, that patterns across many links matter more than any single one, and that human reviewers and spam reports add a manual layer.
In short
- Google is reported to have said in December 2022 that SpamBrain detects both sites that buy links and sites used to pass outgoing links, and neutralises the links it finds.
- Detection works mainly on the selling site, because one publisher that sells links exposes every buyer on it.
- The 2024 leaked Google documentation describes fields that record spikes of similar anchor text and the quality tier of the linking page, but it does not show how they are weighted.
- Google said of its August 2026 spam update that link spam is handled by separate systems, which suggests link detection runs continuously.
- In Editorial.link's March 2026 survey of 518 SEOs, 56% said they believe Google cannot reliably identify paid links.
Google has never published how it detects paid links, and nobody outside the company can see a payment. What it does is infer payment from patterns. The known parts are a machine learning system called SpamBrain, signals in the link graph and in anchor text, and a manual layer of human reviewers and spam reports.
This lesson separates what Google has stated, what leaked documents describe, and what practitioners infer. Treat the three differently.
What Google has said
With its December 2022 link spam update, Google is reported to have said that SpamBrain can detect both sites that buy links and sites used for the purpose of passing outgoing links. Links found this way are “neutralized”, meaning any credit they passed is lost.
Two points follow from that statement. Detection covers both ends of the transaction. And the usual result is not a penalty. Since Penguin 4.0 in September 2016, Google has said it devalues spam links instead of demoting the whole site.
There has been no named link spam update since December 2022. When Google ran its August 2026 spam update, it said the update “does not target link spam” and that link spam is “handled by separate systems”. The reasonable reading is that link detection now runs all the time. That reading is an inference, not a statement from Google.
Google’s link spam updates timeline has the full sequence.
The seller is the weak point
A buyer’s link profile can look tidy. A seller’s site rarely does. A publisher that sells links builds a visible record: article after article linking to unrelated commercial pages with keyword anchors, across niches that have nothing in common.
Once a site is classed as one that sells links, every link it gives can be discounted at once. That is why one bad publisher list exposes many buyers, and why the same inventory sold on several marketplaces is worth less each time it is sold.
These are the patterns on a selling site that anyone, including a classifier, can observe:
- A public “write for us” or “advertise” page with a price.
- Many posts with commercial outbound links and exact-match anchors. A share above 60% is a working red flag in publisher vetting.
- Outbound links to casino, loan or pharmacy pages from unrelated content.
- Five to fifteen posts a day across unrelated categories.
- Rankings for topics that do not match the site’s stated subject.
- An organic traffic collapse after a spam or core update.
How to vet a publisher turns that list into a scoring method.
Signals at the buyer’s end
On the receiving site, the signals are about shape and timing, not individual links.
Anchor text. A natural profile is mostly brand and URL anchors. A profile heavy with exact-match commercial phrases is the classic sign of built links. See anchor text.
Timing. A sudden burst of links with similar anchors, with no news event to explain it, stands out. Link velocity covers what is normal.
Source overlap. If most of your new links come from sites that also link to the same set of unrelated commercial sites, the group is connected in the link graph even when the sites look independent. Analysts describe this graph relationship as the largest link footprint.
Relevance. Links from pages and sites with no topical connection to the target are easier to discount.
What the leaked documents describe
In 2024, internal Google API documentation leaked. It lists fields and modules, not weights, and Google has not confirmed how any of them are used. Analyses by iPullRank and Hobo describe several that relate to this subject:
| Documented in the leak | What analysts infer |
|---|---|
| Fields counting spam-phrase anchors, the days over which they appeared and whether they were demoted | Spikes of similar anchors are measured, and anchors inside the spike can be discounted |
| Penguin-era anchor statistics, including counts of dropped anchors | Suspect anchors are ignored instead of the page being punished |
| A source quality bucket tied to the index tier of the linking page | Links from low-tier pages may count for little or nothing |
| A demotion for anchor mismatch | Off-topic anchors or sources can be discounted |
| A measure of how focused a site is on its topic | Relevance of the linking site is assessed |
The left column is what the documents contain. The right column is interpretation. The leak and antitrust documents on links explains the status of this evidence.
The manual layer
Algorithms are not the only route.
Human reviewers. Google’s webspam team can apply a manual action for “unnatural links to your site” or “unnatural links from your site”. Unlike algorithmic devaluation, this appears in Search Console.
Spam reports. Google accepts reports from the public, including competitors, and says it uses them to improve detection.
Public evidence. Seller price lists circulate as spreadsheets, and marketplaces list their inventory to any registered user. Nothing stops a reviewer from reading the same lists a buyer does.
Two outcomes
| Algorithmic | Manual action | |
|---|---|---|
| What happens | Links are ignored | A reviewer applies a penalty |
| Notification | None | Search Console message |
| Symptom | Links stop working, rankings plateau or slide | Sharp drop for pages or the whole site |
| Fix | Stop the tactic, earn real links | Remove or disavow, then file a reconsideration request |
Google’s Gary Illyes and John Mueller are reported to have said that when a profile is overwhelmingly manipulative, the algorithms can distrust the site’s links as a whole. For the manual route, see link penalties and recovery.
What Google probably cannot see
Detection is not complete, and it is honest to say so. Practitioners largely agree: in Editorial.link’s March 2026 survey of 518 SEOs, 56% said they believe Google cannot reliably identify paid links. An Ahrefs study of the top 110,000 sites, published in May 2020, found the sponsored attribute on about 0.01% of referring domains, so most paid links carry no label.
A single paid placement on a real publication with editorial standards, real readers and a relevant article looks the same as an earned link. What gets caught is scale and repetition: the same sellers, the same anchors, the same pace. This is also why the usual cost of buying links is wasted money, not a penalty.
What this means in practice
- Judge the publisher’s outbound profile before your own link. You inherit its record.
- Avoid inventory that every buyer can see, such as a link marketplace list sold unchanged to all.
- Keep anchors mostly brand and URL.
- A
sponsoredattribute removes the policy risk, at the cost of ranking credit. - Do not treat absence of a penalty as proof that links are counting.
Where to go next
How to buy backlinks safely applies this to purchasing decisions. Terms such as SpamBrain, manual action and neutralised link are defined in the glossary.
Common questions
Can Google tell if a link was paid for?
Not by seeing the payment. Google infers it from patterns, such as a site whose articles link out to unrelated commercial pages with keyword anchors. A single well-placed paid link on a real site is hard to tell apart from an earned one.
What is SpamBrain?
SpamBrain is Google's machine learning system for spam detection. Google is reported to have said in December 2022 that it is used to detect sites that buy links and sites used to pass them on.
What happens when Google detects a paid link?
Usually the link is ignored and passes no credit, with no notification. If paid links dominate a profile, a human reviewer can apply a manual action for unnatural links.
Does a sponsored attribute protect me?
Yes. A paid link with rel="sponsored" or rel="nofollow" is allowed under Google's spam policies. It is treated as advertising, not as a ranking signal.
Do competitors report paid links?
They can. Google accepts spam reports from the public and says it uses them to improve its detection systems. A report does not guarantee action on a single site.
