How Does a Google Backlinks Tool Work?

A backlinks tool doesn't ask Google anything. It runs its own crawler, builds its own map of links between websites, and shows you that map with metrics it invented itself. That's why every tool gives you a different number for the same website, and why none of them can tell you exactly what Google is doing with your links.

What a backlinks tool is doing behind the scenes

People assume tools like Ahrefs, Semrush, or Moz plug into Google somehow. They don't. Google doesn't hand out its link data to third parties, full stop. What each tool has instead is its own web crawler, a piece of software that behaves a bit like Googlebot but is owned by that company, following links from page to page and recording what it finds.

Ahrefs runs a crawler called AhrefsBot. Semrush runs SemrushBot. Moz uses its own crawler called Rogerbot. Each one crawls the open web independently, at its own speed, on its own schedule, and stores what it finds in its own database. When you type your domain into any of these tools, you're not seeing Google's link graph. You're seeing that company's private copy of the web, filtered down to links pointing at your site.

This is the bit most articles on this topic gloss over: the "backlinks" you see are only the backlinks that particular crawler managed to find before you looked. If a link was published on a small blog last week and none of the big crawlers have visited that blog yet, it simply won't show up. Not because it doesn't count. Because nobody's robot has seen it yet.

How the crawl gets built

Each tool's crawler works through a queue of known URLs, visits a page, reads every link on it, and adds any new URLs it finds to the queue for later. Ahrefs has stated publicly that its crawler processes trillions of known pages and revisits popular, frequently-changing sites (news sites, big retailers) every few hours, while a small business site with low traffic might get recrawled once every few weeks. That gap matters enormously. If a journalist links to your bakery from a local news article on a Tuesday, and the crawler doesn't pass by that page again until three weeks later, your backlink report will look unchanged for three weeks even though the link has been live and working the whole time.

Once a link is found, the tool records a set of details: the linking page, the target page, the anchor text used, whether the link is dofollow or nofollow, when it was first seen, and whether it's still there on the last check. Multiply that across billions of pages and you get the database these tools query when you search a domain.

A worked example

Say you run an independent bookshop website. You check three tools on the same afternoon and get three different answers:

• Ahrefs shows 63 referring domains and a Domain Rating of 24
• Semrush shows 41 referring domains and an Authority Score of 19
• Google Search Console, under Links, shows 12 external linking sites

None of these numbers is wrong. Ahrefs and Semrush have crawled different corners of the web and found different links, some of which the other tool hasn't reached yet or has already dropped because the linking page went 404. Search Console's number is lower because Google only shows you a sample, not the full list, and because Google's own systems have decided some of those links carry so little weight they're not worth surfacing at all. That gap between 63 and 12 is the single most useful thing this exercise teaches you: third party tools are estimates of the web, not a readout of Google's index. For another angle on where links come from, see how to check backlinks inside Google Analytics.

What DR, DA, and Authority Score measure

This is the part worth being blunt about, because it's the bit that gets skipped in most explainers. Domain Rating, Domain Authority, and Authority Score are not Google metrics. Google has never confirmed using anything called Domain Authority. These scores were built by the tool companies themselves, using their own formulas, based on the size and quality of the link graph they've crawled, scaled to a number between 0 and 100 so it's easy to compare sites at a glance.

That doesn't make them useless. A site with a DR of 70 does tend to rank better than a site with a DR of 10, because the underlying signal, being linked to by lots of other well-linked sites, does correlate with how Google's own PageRank-style system behaves. But treating DR as if it were a Google score is a mistake I still see people make on client calls in disguise as excitement: "we got our DA up to 35, we should be ranking number one by now." The tool measures link volume and quality as it perceives it. Google measures hundreds of other things at the same time, including content relevance, user behaviour, and the technical health of your site, which is exactly the territory covered in a full breakdown of technical SEO's key elements.

Why the numbers never match, and why that's fine

Three things cause the mismatch every time:

• Crawl coverage: no crawler sees the whole web, and each one prioritises differently based on its own algorithm for what's worth visiting
• Crawl frequency: a big authoritative site gets recrawled far more often than a small niche blog, so freshness varies wildly
• Link filtering: tools drop links they judge to be spam, dead, or duplicate, and each tool has its own threshold for what counts as spam

If you're using one of these tools to check your own site or size up a competitor, the fix is simple: pick one tool and stick with it for consistency, then treat the numbers as directional rather than exact. Watching whether your referring domains go from 40 to 70 over six months tells you something real. Comparing your 40 against a competitor's 41 from a different tool tells you almost nothing.

If you'd like someone to read those numbers with you and say what is worth acting on, that's the kind of work I do through my SEO services for Google and AI search.

Step by step: how to pull a useful backlink report

1. Enter your domain (or a competitor's) into the tool's backlink checker
2. Sort by Domain Rating or Authority Score, highest first, so you see your strongest links at the top
3. Filter out nofollow links if you want to see what's likely passing ranking value
4. Check the "first seen" and "last checked" dates, because a link marked as live from eight months ago with no recent check could already be dead
5. Export the referring domains list and cross-reference it against Google Search Console's own Links report under the Search Console sidebar
6. Flag anything from an obviously irrelevant or spammy site (gambling directories, link farms, foreign-language content with no connection to your niche) as a candidate for a disavow file

That cross-check against Search Console in step 5 is the step almost everyone skips, and it's the one that tells you what Google itself has registered, even in sample form. A handful of free tools that make this kind of checking easier without a signup are collected on my free tools page.

Where backlink tools earn their keep

The strongest use of any backlinks tool isn't checking your own site, it's checking someone else's. Point one at a competitor and you can see exactly which sites are linking to them, which of those sites might link to you too, and which content of theirs earned the most links, which is the exact discipline covered in competitor tracking for SEO. If a competitor's guide on shipping costs picked up 30 links from small business blogs, that's a strong signal that a similar, better piece from you could earn the same attention, tying straight back into how content marketing and SEO work together to build links naturally rather than buying them.

Local businesses often overlook that citations and directory listings, the kind covered in a full breakdown of what local SEO includes, are backlinks too, and a decent tool will show you which directories you're missing compared to competitors in your postcode.

The uncomfortable bit

None of these tools can see what Google's algorithm does with a link once it's found it. A link from a small niche blog with a DR of 8 might carry more real ranking weight in Google's eyes than a link from a bloated DR 60 directory stuffed with ten thousand outbound links on every page, because Google's own systems weigh relevance and trust in ways no third party crawler can replicate. Tool companies will happily sell you the idea that a high DR link is automatically worth chasing. Sometimes it's worth less than a scruffy, relevant one from a real site with real readers. If you're building a link strategy around AI-written outreach or automated link building, it's worth reading how to use AI for SEO without getting penalised before you scale anything up, because Google's spam systems are increasingly good at spotting manufactured link patterns even when the DR looks impressive.

If you're looking for places to publish, I keep a free list of guest posting sites that's checked live.

Related: link building: guidelines and how to pitch.

Related: my guest posting sites usa page.

For the full free method, see my guide to checking how many backlinks a site has.

I run AI training and workshops for teams, and help businesses with AI enablement and workflow automation, so the busywork runs itself and people get time back. Most of that work is with SaaS marketing teams and small businesses. Here's how we can work together.

How crawlers build an index, according to the vendors

Backlink tools share a basic design. A crawler moves across the web, records the links it finds on each page, and stores them in an index. When you look up a domain, the tool reads from that stored index, not from the live web, which is why every result has a delay built in.

Vendors describe their indexes differently, and these are their own claims:

• Ahrefs says its backlink index is updated with fresh data every 15 minutes, and claims its crawler is the most active after Google's.
• Moz says newly discovered linking domains can be populated into its Link Explorer index in about three days.
• Majestic says it runs a Historic Index and a smaller Fresh Index. It states that it updates the Historic Index monthly and aims to update the Fresh Index daily, and that the Historic Index takes many days to build, so it's always a few days behind.

Discovery depends on the page doing the linking. Moz explains it may take longer to find backlinks depending on how crawlable the referring pages are, and that its index may miss a link if the referring page isn't crawlable or is low quality. If Moz hasn't indexed the linking page, that link won't appear at all.

The honest limits: none of these vendor claims is independently audited, and no index covers every link on the web. Each crawler takes its own path, which is why the same site shows different totals in different tools. Majestic's FAQ wording may also be dated, and it shows the index build date in its site footer so you can see how current the data is.

So treat any count as a single vendor's view at a moment in time. If a link you expected is absent, the reasons links go missing from reports goes through the causes. For making sense of your backlink total, there's a separate guide, and our main backlink checker page covers every way to check.

Frequently asked questions

Do backlinks tools pull data directly from Google?

No. Every major backlinks tool runs its own independent web crawler, separate from Googlebot, and builds its own database of links. None of them have access to Google's actual link index, which is why the numbers differ between tools and never perfectly match Google Search Console.

Why does my backlink count differ between Ahrefs, Semrush, and Search Console?

Each source has crawled a different slice of the web at a different time. Third party tools also filter out links they judge to be dead, spammy, or duplicate, using their own rules, while Search Console shows only a sample of the links Google itself has chosen to surface.

Is Domain Rating or Domain Authority a Google ranking factor?

No. Both metrics were invented by the tool companies themselves as an estimate of link authority, and Google has never confirmed using either one. They correlate loosely with ranking ability because they're built on similar principles to how Google weighs links, but treating them as an official Google score is a mistake.

How often should I check my backlinks?

Once a month is enough for most small businesses. Checking weekly rarely shows meaningful change because crawlers don't revisit smaller sites that often, and chasing daily fluctuations in referring domain counts will waste time you could spend earning new links instead.