SpamBrain is one of the few machine-learning systems Google names publicly. It sits behind spam updates and link spam updates, and it is often blamed (sometimes wrongly) for sudden ranking losses. Yet the amount Google has actually disclosed about it is small.
This guide sticks to what is on the record: how Google describes SpamBrain, the figures it shared in its webspam reports as covered by the search press, how SpamBrain relates to link spam, and the honest limits of public knowledge. We finish with a practical checklist for staying on the right side of it.
Key Takeaways
- Google describes SpamBrain as its AI-based spam-prevention system and lists it among its spam detection systems.
- According to Search Engine Land's coverage of Google's 2022 webspam report, SpamBrain launched in 2018 and in 2022 caught about five times more spam sites than in 2021.
- Google credited SpamBrain with detecting link spam, including in the December 2022 link spam update.
- When links are neutralised, Google says the ranking benefit they gave is lost — there is nothing to “recover”.
- Google does not publish SpamBrain's signals, thresholds or model design. Treat claims about its inner workings with caution.
What Google says SpamBrain is
“SpamBrain is our AI-based spam-prevention system.”
— Google Search Central, Google Search spam updates and your site
That sentence on Google's spam updates page is most of the official definition. The ranking systems guide adds that Google uses a range of spam detection systems, including SpamBrain, to deal with content and behaviour that violate the spam policies, and that these systems are updated regularly as spam tactics change. A spam update is Google's term for a notable improvement to those systems.
What Google has disclosed so far
Most public detail comes from Google's annual webspam reports. The figures below are as reported by Search Engine Land in April 2023 from Google's 2022 report; we have not seen later official figures that replace them.
| Disclosure | What was reported | Source |
|---|---|---|
| Launch | SpamBrain debuted in 2018 | Search Engine Land, Apr 2023 |
| Year-on-year | About 5x more spam sites caught in 2022 than in 2021 | Search Engine Land, Apr 2023 |
| Since launch | About 200x more spam sites detected than at launch | Search Engine Land, Apr 2023 |
| Link spam | After the Dec 2022 link spam update, 50x more link spam sites detected than after the July 2021 update | Search Engine Land, Apr 2023 |
| Hacked spam | Detection of hacked spam improved about 10x | Search Engine Land, Apr 2023 |
| Timing | Spam can be detected during crawling, before indexing | Search Engine Land, Apr 2023 |
| Overall claim | Google says 99% of visits from Search are spam-free | Search Engine Land, Apr 2023 |
“SpamBrain now detects spam during the crawling process”
— Search Engine Land, Google webspam report: SpamBrain caught 5x more spam
That last point matters: some spam may never reach the index at all, which means you will not always see a “drop” — the pages simply never rank.
SpamBrain and link spam
Google's two confirmed link spam updates are the July 2021 link spam update (26 July – 24 August 2021) and the December 2022 link spam update (14 December 2022 – 12 January 2023). For the December 2022 release, Google said it was using SpamBrain to detect both sites buying links and sites used to pass outgoing links. See our write-up of the December 2022 link spam update.
The effect of being caught is neutralisation, not punishment in the traditional sense. Google's spam updates page is explicit that once spammy links are neutralised, the benefit they produced is gone. That is why the useful response is to change how you earn links, as covered in link building after link spam updates.
If you saw a drop that lines up with a link spam update, our link spam update recovery guide explains how to separate lost link value from other causes. Remember that many link-heavy sites are also affected by core updates; the comparison in core updates vs spam updates helps you tell the difference before you act.
SpamBrain and scaled or AI-generated spam
In March 2024 Google introduced the scaled content abuse, expired domain abuse and site reputation abuse policies. Google has not published a breakdown of which system enforces which policy, so we cannot say SpamBrain specifically enforces scaled content abuse. What we can say is that Google's spam detection systems — SpamBrain among them — deal with content that violates its policies, and that scaled content abuse applies however the pages are produced. See the scaled content abuse policy.
The limits of what is public
Search for SpamBrain and you will find confident claims about the exact signals it uses. Google has not published them. Here is a fair split:
| Known (Google or reputable coverage) | Not public / speculation |
|---|---|
| It is AI-based and part of spam detection systems | The model architecture or training data |
| It has been used to detect link spam and hacked spam | Specific link patterns or thresholds that trigger it |
| It can act during crawling | Whether it scores individual pages, sites or networks in each case |
| Spam updates are announced on the dashboard | Exactly which update changed which part of SpamBrain |
How to stay clear of SpamBrain: a checklist
- Audit links you control. Stop paying for links that pass ranking credit; mark sponsored and affiliate links with
rel="sponsored"orrel="nofollow". Our backlink audit guide explains the review. - Check for hacked content. Look for unfamiliar URLs in Search Console and server logs, and fix vulnerabilities.
- Review scale. If you publish many similar pages, make sure each offers distinct value.
- Review third-party content hosted on your domain against the site reputation policy.
- Moderate user-generated content to remove spam comments and profiles.
- Document fixes and allow time — Google mentions a period of months of compliance.
Common mistakes
- Blaming SpamBrain for every ranking drop. Most drops relate to core updates, competition or technical issues.
- Buying “SpamBrain-safe” link packages. No such thing is verifiable.
- Mass-disavowing natural links out of fear.
- Assuming AI-written content is automatically spam. Google targets scaled, low-value content regardless of how it is made.
- Treating webspam report numbers as current-year figures.
Related Guides
- Neural Matching Explained: How Google Connects Concepts
- Google's Original Content Systems and the 2019 Original Reporting Change
- Google's Site Diversity System: Why One Site Rarely Gets More Than Two Results
Frequently Asked Questions
Is SpamBrain a penalty?
It is an automated detection system. Sites it flags can be demoted or have links neutralised, but there is no Search Console notification as with a manual action.
When did SpamBrain launch?
Search Engine Land's coverage of Google's 2022 webspam report says it debuted in 2018. Google described it publicly in its webspam report for 2021, published in April 2022.
Does SpamBrain detect AI content?
Google has not said it targets AI content as such. Its policies target scaled, low-value content however it is produced.
Can I recover from SpamBrain?
If you remove violations, Google says improvement may follow after months of compliance. Benefit from neutralised links does not come back.
Is SpamBrain used in every spam update?
Google has not said this explicitly for each update. It describes spam updates as improvements to its spam detection systems, which include SpamBrain.
Conclusion
SpamBrain is powerful, but it is not mysterious in what it wants: no manipulative links, no scaled junk, no hacked pages. Build a site that would pass a human review and you have little to fear. If you think spam systems are suppressing your site, our penalty recovery service can audit it — get a quote.
