Why Google Indexes Pages It Can’t Crawl: Understanding Robots.txt, Noindex, and Backlinks
As SEOs, we often believe that if we’ve blocked a page via robots.txt or added a “noindex” tag, it’s effectively invisible to Google. However, many webmasters have experienced a strange scenario where Google indexes pages that are supposedly blocked from crawling.
What’s happening here? Why does Google index pages it can’t even see? Let’s break this down.
Crawling vs. Indexing: Two Different Things
Before we dive into why Google is indexing blocked pages, it’s important to understand the distinction between crawling and indexing.
- Crawling is when Googlebot (or any search engine crawler) fetches a page from your website to read its content.
- Indexing is when Google decides to store that page in its search index so it can be shown in search results.
Here’s the catch: a page can be indexed even if it hasn’t been crawled.
That’s right. Google can add a page to its index based on certain signals (like backlinks) even when it can’t crawl or read the page’s content. This is what leaves many webmasters scratching their heads.
The Role of Robots.txt in Blocking Crawling
When you add a URL or section of your site to the robots.txt file with a “Disallow” rule, you're essentially telling Googlebot, "Don't crawl this page." And Google, by and large, obeys that command. The crawler won’t visit the page, and it won’t retrieve any content from it.
However, blocking crawling doesn’t stop indexing. Google can still know that a page exists without being able to crawl it. How? It can discover the page through other means, such as:
- Backlinks from other sites
- Internal links from pages on your own site that aren't blocked
- Other forms of indirect discovery, like XML sitemaps
In these cases, Google knows that the URL exists, even if it can’t view its content. And this is where things get complicated.
Why Would Google Index a Page It Can’t Crawl?
If Google can’t see the content on a blocked page, why does it bother indexing it at all? Here’s where the magic of backlinks comes into play.
Backlinks, or inbound links from other websites, act as signals to Google. They tell the search engine, “Hey, this page is important enough for someone to link to it.” In some cases, this can be enough of a reason for Google to index a URL, even if it can’t see the content.
Think of it like this: if you were walking through a library and saw a bunch of people recommending a book but weren’t allowed to open the book yourself, you might still assume that the book has value based on the recommendations alone. Similarly, if a page has backlinks, Google assumes there’s value—even if it can’t crawl the page to verify.
This happens even if:
- The page is blocked in robots.txt.
- The page has a "noindex" tag that Google can’t see due to the robots.txt block.
Google's decision to index the page is based on the existence of external signals (like backlinks), not the content itself.
The Importance of Backlinks in Google's Indexing Decisions
This leads us to an important takeaway: backlinks are still incredibly valuable in Google’s eyes.
Even though modern SEO best practices prioritize quality content and user experience, backlinks still play a significant role. In fact, Google often uses backlinks to assess the importance or relevance of a page when it lacks other signals (like content, due to a crawl block).
For example, if a government website blocks certain pages from being crawled but those pages have plenty of high-quality backlinks, Google may still index them because of the perceived value to users.
Should You Worry About These Indexed-But-Blocked Pages?
Most of the time, you shouldn’t lose sleep over this. When a page is indexed but blocked by robots.txt, the average user won’t see it in the search results, and it’s unlikely to rank well. Google prioritizes content it can actually crawl and understand.
However, seeing these pages indexed in tools like Google Search Console can cause confusion. Webmasters might worry about the impact on their site’s overall SEO performance or feel frustrated about spammy URLs (e.g., query parameters) being indexed.
How to Manage This Issue
If you’re dealing with a similar situation, here are some practical steps you can take:
- Use "Noindex" Without Robots.txt: If you want to prevent a page from being indexed entirely, the best approach is to use the "noindex" tag without blocking it in robots.txt. This allows Google to crawl the page, see the "noindex" directive, and exclude it from the index.
- Handle Spammy URLs Proactively: If bots are generating spammy URLs that are being indexed, consider returning a 403 (Forbidden) status for those pages, which prevents them from being accessed or indexed.
- Ignore Non-Issues: In many cases, having a few indexed-but-blocked pages won’t hurt your site’s SEO performance. It’s more of an annoyance than a real problem. Focus on your site’s overall content quality and user experience, and let Google handle the technical nuances.
Final Thoughts: Don’t Panic Over Indexing Anomalies
While it can be frustrating to see blocked pages indexed, Google’s indexing behavior is driven by a combination of backlinks, crawl directives, and content availability. When faced with these situations, remember that backlinks still carry weight, and Google often treats them as signals of importance.
So, while it’s important to maintain control over your site's crawling and indexing policies, don’t panic if a few blocked pages show up in the index. Focus on the bigger picture of providing great content and earning quality backlinks, and your SEO will remain in good shape.
By understanding the nuances of how Google crawls and indexes your site, you can make smarter decisions about your SEO strategy—without getting bogged down by the technical quirks of bots and backlinks.
Acknowledgment
This article was inspired by a conversation within the SEO community on LinkedIn. Read full conversation here.