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Fri. Jan 15th, 2021
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Every backlink tool will save various links.

When developing an index of the web, business need to make numerous options around crawling, parsing, and indexing information. While there’s going to be a great deal of overlap in between indexes, there’s likewise going to be some distinctions depending upon each business’s choices.

In the name of openness, we wish to let individuals understand more about Ahrefs’ link index.

Links take users from one web page to another when clicked. There are numerous methods to develop them, with the most typical approach being the classic HTML << a>> component with an href quality.

<< a href="">> link text<

Nevertheless, it's possible to develop relate to other aspects, consisting of:

  • Onclick
  • Button
  • Ng-click
  • Option/value
  • And more ...

In a perfect world, anything that works as a link would be saved. Sadly, we do not reside in a perfect world. Neither Ahrefs nor Google shops all kinds of links since it's not an effective procedure to pack each page and click every link. That's precisely what you 'd need to do if you wish to discover all of the links that work for users.

Rather, spiders usually bring pages, perhaps render them, then extract and shop different kinds of links. All spiders work in a different way, so let's discuss how we do things here at Ahrefs.

Hyperlinks we save

Here are the kinds of links we save in our index.

External links

Hyperlinks from one site to another produced utilizing the classic HTML << a>> component with an href quality.

Internal links

Hyperlinks from one page on a site to another page on the very same site. There are 22.21 trillion internal backlinks in our index. That's even more comprehensive than our live external link count. We're the only SEO tool where you can access this information without a customized site crawl. We utilize the internal link information in the URL Rating (UR) estimation, comparable to how Google would utilize it in their PageRank estimation.

If you wish to see when we initially and last crawled a URL, you can examine the "Best by links" report inSite Explorer There are tabs for both External and Internal Hyperlinks.

best by links report

Hyperlinks we might save

Here are all the links we save under some scenarios.

Hyperlinks placed with JavaScript

Since Google renders all pages, they can count links that are placed with JavaScript however aren't in the HTML code. Making at scale takes a lot more resources than simply downloading the HTML of pages. At Ahrefs, we render around 80 million pages each day. That's why we will have a few of these links placed by JavaScript, however not all of them. We're presently the only SEO tool that renders throughout our routine crawling of the web, so we have some link information that other tools do not have.

Nevertheless, we just count links placed with JavaScript if they remain in the format of an HTML << a>> component with an href quality. You'll see these links tagged in the backlinks report as " JS," like this:

js link

Hyperlinks from pages with URL criteria

Specifications are additions to a URL like? tag= something. You might see a few of these URLs in our index, however they're generally criteria that reveal various material. In most cases, pages with criteria can reveal the very same material. We have numerous systems in location to combine URLs to canonical variations and extra security for boundless crawl courses. Other tools might not make the very same choices or have the very same defenses in location. As an outcome, they might count basically the very same link numerous times.

Hyperlinks we attempt not to shop

Here are the links we do our finest not to shop.

Hyperlinks from pages with URL criteria

As pointed out above, there are great and bad kinds of criteria. We attempt not to save the ones that are duplicated.

Hyperlinks from pages in boundless crawl courses

These courses develop a limitless variety of possible URLs. Specifications are one method they might form however so are filters, vibrant material, and damaged relative courses for links. As pointed out in the past, we have numerous defenses in location for links on these kinds of pages so that they're less most likely to appear in our reports. Appreciating canonicalization and the method we focus on crawling pages are simply 2 of those defenses. Every index will need to handle these boundless areas, however there's capacity for these pages to pump up link counts.

Hyperlinks we do not shop

Here are all the links we never ever save.

Hyperlinks in PDFs or other files

Google transforms numerous file formats to HTML and indexes them as they would any other page. This indicates that they count links in these files. I do not think that any SEO tool presently indexes these links, however we most likely should. I believe that a person day we will, however I'm likewise worried that the effort and resources needed for this will not deserve it. According to Google Web Designer Trends Expert John Mueller, links in PDFs don’t have any practical effect in web search

Hyperlinks in iframes

Iframes permit another page to reveal within a page. Since of this, Ahrefs does not count links in iframes. Nevertheless, they are revealed to users, so other tools might count them despite the fact that the material technically comes from a various page. Google might or might not count these links.

Hyperlinks from pages not indexed

We drop these links. There are combined messages from Google agents on whether they utilize these in link estimations or not. Various tools might alter choices.

Exact same links from numerous IPs

One enjoyable truth about the web is that websites might serve the very same page from numerous IP addresses. If this holds true, a link index might count the very same link numerous times. We do not do this. We associate relate to the pages they are on.

Several links to the very same page from a single page

Presently, we just tape-record one variation of a link on a page. If you connect to a page in the menu and after that once again in the body material, we will just count among these links. We might alter this in the future to provide users more information, however this is the present state. Google will count all variations of links for passing PageRank however might just utilize one variation's anchor text.

Other link associated products that affect the index

Comprehending how we count links is something, however numerous other things can impact what does and does not get counted.

Variety of links per page

I do not think we have a limitation for the variety of links we count per page, however we do have a page size limitation that might ultimately affect the variety of links we see. Google suggests no more than a few thousand links per page.

Rerouted or canonicalized

At Ahrefs, we rely on all redirects and canonical tags and combine links where sites inform us to. For Google, this is more made complex as they have numerous canonicalization signals that identify which page is the lead in a canonical cluster. We keep things easy since it's difficult to understand how Google views every scenario, and it would puzzle our users if we dealt with canonicals and reroutes in a different way every time.

These links are tagged in our reports with "301", "302", or "Canonical," such as:

Which domains get indexed?

In Ahrefs, we have the Referring domains report that reveals all the domains connecting to a site or web page.

However how precisely do we count domains?

You would believe this would be a simple concern to address. It's simply, right? Sadly, things are a little bit more intricate as there are numerous methods to count domains. One choice is to deal with every authorized domain as a domain-- which appears to be how Google aggregates them inGoogle Search Console Another is to deal with every subdomain as a various domain. You might likewise aggregate some areas of a website and not others (what Google does), pass every area on a various tech stack, and so on. There are numerous choices.

At Ahrefs, we have ~175 million domains post-vetting. The vetting procedure consists of getting rid of spam domains and breaking out some subdomains where we have actually identified that various users manage the various locations. We utilize a customized list for this, however there's a rather comparable public list at

ahrefs domains

It is very important to keep in mind that various domain meanings can lead to big variations of referring domains. Here are some examples of things that others, not Ahrefs, might count as different domains:

  • Mobile variations subdomains (,, and so on)
  • Country/Language subdomains (,,,, etc). There might be exceptions to this in our index, such as, however this is not basic practice.
  • Random subdomains (,, and so on)

Another choice backlink tool companies need to make is whether they ought to count some subfolders as various domains. For example, I believe most connect indexes would count various blog sites on widely known platforms (e.g.,, as various domains since various users manage them. However why refrain from doing the very same for websites like or At Ahrefs, we do not presently do this, however there's a possibility we might in the future where we understand various individuals manage each subfolder on a website.

The point here is that there are numerous methods to count domains. That's apparent when you take a look at the differing figures from business that count websites on the web. According to Verisign, there are 370.7 million signed up domains in Q3 2020 throughout all TLDs. According to Netcraft, there are 1,229,948,224 websites throughout 263,787,870 distinct domains with 193.8 million active websites in November2020 According to Internet Live Stats, there are approximately 1.8 billion sites with less than 200 million presently active. Each business plainly has a various method for counting domains.

To evaluate, what we do at Ahrefs is take all the websites we understand about and eliminate numerous spam and non-active domains, then include some for subdomains on websites like That's how we pertain to our overall domain count of ~175 million. Other indexes might do this in a different way and create various counts.

Why we can't see all links

As we discover backlinks by crawling the web, we can just do so on websites we're enabled to crawl. If website owners obstruct AhrefsBot in their robots.txt file, we can't crawl their website. For instance, if you get a backlink from and obstructs AhrefsBot, we can't crawl their website and your backlink will not appear in Ahrefs. IP obstructs, user-agent blocks from servers (various from robots.txt), server timeouts, bot security, and numerous other things can likewise impact our capability to crawl some sites. Crawling the web at scale isn't simple.

We have numerous link indexes

Each tool needs to make choices about information storage and retrieval. At Ahrefs, we divided our information into numerous indexes.

  • Live -- the links we see that are still active on the internet. This finest represents the present state of the web and is what a lot of our users will discover most helpful.
  • Current -- links we have actually seen active on the internet in the previous 3-- 4 months.
  • Historic -- all the links we have actually ever seen. This is going to be the most thorough list, however with numerous links that no longer exist.

You can change in between indexes in our backlink and referring domain reports.

ahrefs indexes

Other indexes might select to reveal all the information they have actually ever seen, and while this indicates they might reveal a great deal of links, a lot of those links might not exist any longer.

Last ideas

We desired you, our users, to have more info on our index so that you can make educated choices. We likewise desire you to let us understand if you believe we ought to alter things and why.

If you're presently comparing link indexes or have concerns about our information, do not hesitate to connect to us with any concerns or for explanations.

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