Different backlink tools report different numbers for the same domain because they're measuring through different, partial indexes — not because one of them is broken. Here's what that means for how you should actually use the data.
Run the same domain through three different backlink tools and you'll get three different numbers — sometimes by a small margin, occasionally by an order of magnitude. This surprises people who assume backlink count is an objective fact about the web, discoverable the same way regardless of who's measuring it. It isn't. It's the output of a specific crawler with a specific index, and different vendors' crawlers see different, overlapping-but-not-identical slices of the actual link graph.
Why the Numbers Actually Disagree
No Crawler Sees the Whole Web
Every backlink data provider maintains its own index, built by crawling a finite set of URLs on its own schedule. None of them crawl the entire web, and none of them recrawl every known page with the same frequency. A link that exists on a page your chosen provider hasn't recrawled recently simply won't show up yet, even though it's live right now if you visited the page yourself. Two providers with different crawl schedules and different historical crawl depth will, correctly, report different link counts for the identical real-world state of the web — neither is "wrong" in the sense of malfunctioning; they're measuring through different, partial windows.
Authority Scores Aren't Comparable Across Vendors
A domain authority or domain rating type score is a proprietary model, specific to the vendor that computes it, built on that vendor's own index and its own weighting of the signals it's chosen to include. A 40 from one tool and a 40 from another are not the same measurement any more than two different companies' internal "customer satisfaction scores" measured on a 1–100 scale would be directly comparable — the scale is shared; the underlying model isn't. Comparing your score on Tool A against a competitor's score on Tool B is comparing two different instruments, not two readings of the same thing.
Different Definitions of What Counts
Whether nofollow links are included, how a provider deduplicates multiple links from the same referring page, how aggressively it filters what it judges to be low-quality or spam domains before reporting a count — these are methodology choices, not universal standards, and they materially change the resulting number. A tool that filters aggressively will report a smaller, arguably "cleaner" count than one that reports everything it finds; both are internally consistent, and neither is the single correct answer.
The Practical Implication: Stop Cross-Vendor Comparisons
Once the measurement is understood to be provider-specific rather than a shared objective fact, the right way to use backlink data changes. Comparing your domain's number from one provider against a competitor's number pulled from a different provider is not a valid comparison, even though it's an extremely common one — it looks like a fair fight and isn't. The valid comparison is your number against the same competitor's number, from the same provider, checked the same way. And the valid trend is your own number, from a single consistent source, over time — not a cross-vendor snapshot, a within-vendor series.
What's Actually Worth Watching in Backlink Data
Held to a single consistent source, backlink data is genuinely useful for a narrower set of questions than "what's our score": whether total referring domains is trending up, flat, or down over a period that matters to you; whether a sudden spike in low-quality or clearly unnatural-looking links has appeared, which is the kind of anomaly worth investigating regardless of what it does to an aggregate count; and, when comparing against a competitor on the same provider, whether the gap between you is widening or closing. All three are trend questions, answerable within one consistent data source, and none of them require treating the absolute number as ground truth.
This is the same discipline that applies to rank tracking: a single snapshot from an inconsistent source is close to unusable; a consistent series from one source, read as a trend, is where the actual signal lives.
Where This Data Comes From in SearchVitals
SearchVitals' backlink snapshots are built on DataForSEO's live index rather than a blended or estimated figure, and every audit uses the same source consistently, so a trend line you build inside the product is comparing like with like across checks. It won't match a number from a different provider, for the reasons above — and it isn't supposed to. It's built to be internally consistent, which is the property that actually matters for tracking change over time. For the broader picture of how backlinks factor into rankings, see our Backlinks & Rankings guide.