Study: Who Has the Largest Index of Links?

An essential part of any strong SEO program is having third parties link to your site. In addition to the SEO benefits, getting linked to by third parties is also a great way to build your brand and stay highly visible across the web. For this reason, using backlinking tools is important.

Getting access to more link data is generally good, but which tool provider has the largest index? Today’s post will talk about the outcome of a study that addresses this topic.

Disclosure: My employer, Perficient, was contracted by Moz to perform this study. The terms of the agreement between Perficient and Moz clearly state that Perficient would conduct the study independently of Moz and write up the results based on what we saw in the data. In short, Moz influenced the decision to conduct such a study, but the conclusions in this post are 100% our own, with no influence by Moz.

Our goals for the study were to:

1. Evaluate link index size across an array of domains using summary data pulled from each provider’s APIs. The backlink tool providers included in this study were: Moz Link Explorer, ahrefs, Majestic, and SEMrush. Our evaluation considered both linking domains and linking pages found.
2. Confirm the API level analysis by pulling detailed link data. This included pulling all the links for 28 domains split into three markets: Technology, Health, and Finance.
3. Perform cross-validation checks to determine:
   • How well each tool performs routine deduping of link data and if it reports the same link in more than one form. Examples include:
   • • https://www.yourdomain.com/link-page/
     • http://www.yourdomain.com/link-page/
     • http://yourdomain.com/link-page/
     • http:// yourdomain.com/link-page
   • If the link totals reported by the API agree with the link totals you see when detailed links are downloaded.

Link Index Size – API Data

Perficient selected 3,000 queries across the Technology, Health, and Finance market sectors (1,000 queries per sector). These queries were sourced without input from Moz. They were randomly drawn from the query set that Perficient has historically used in its annual Links as a Ranking Factor studies. We pulled the Google results for these queries and built a list of the domains ranking in the top 100.  Next, we deduped the list down to a set of 85,308 domains.

Next, we made API calls to each of the four vendors to see how many linking domains and linking pages each party reported and analyzed the results. First, we analyzed the raw tabulation of the total links reported by each of the APIs:

In this view, Moz reports roughly 90% more links than Majestic, which reported the second-largest total in this test.

Next, we wanted to determine what percentage of the time each vendor reported the most links on a per domain basis. To do this, we analyzed the comparative link volumes for each vendor across all 85,308 domains to see how many times each party reported the most, the second most, the third most, and the least links:

Moz reported the most linking pages over 48% of the time, so it seems that the link index size differential appears across various domains. SEMrush scored second in this test, reporting the most linking pages nearly 22% of the time in our test set.

Finally, we looked at which vendor reported the most linking domains across all 85,308 domains:

Again, Moz reported the most linking domains nearly 60% of the time.

Link Index Size – Manually Pulled Data

We manually downloaded the links for each vendor. The full link files from SEMrush could not be pulled, so we did not include them in this part of the study.

The full link data set for Moz is not available through a general-public API, so we had to make a special request. I asked Moz to comment on their plans to make that data available to the general public. They said:

While we currently do not expose our full link data via our API, custom, enterprise-grade plans are available for companies that require more link data and complete access to the Mozscape link index.

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Please note that access to plans with the complete data requires a custom quote. You can learn more about that here.

Here is what our analysis of the technology market sector websites found:

Moz reported the most linking pages 78% of the time and the most linking domains 67% of the time. Ahrefs had the second strongest scores.

Health site scores were as follows:

Again, Moz came out on top with the most linking pages 70% of the time and the most linking domains 80% of the time. Ahrefs also came in second in this category.

Here is a look at Finance, our final category:

Majestic and Moz tied for the lead in reporting the most linking pages, but Moz reported the most linking pages for the sampled Finance sites 100% of the time.

We took one more slice at that and tabulated the total links found by category:

By this metric, Moz shows the most links for Technology and Health, and Majestic shows the most for Finance.

For our final analysis, we reviewed how many duplicate links each vendor provided that could have been filtered out but weren’t. To do this, we followed this process:

• All linking pages were stripped of “https://” or “http://” (if present).
• All linking pages were stripped of “www” (if present).
• All linking pages were stripped of a trailing “/” (if present).
• The remaining total was subtracted from the total links to determine how many duplicates were removed during this process.
• The sum was then calculated as a percentage to create a % of duplicate links detected score.

Here are the results:

Majestic won this category with a duplicate links detected level of 4.8%. Moz trailed closely behind at 5%.

Summary

Based on this data, Moz appears to have the largest link data set among the tools tested. Remember, this was a limited dataset, and results can vary significantly based on how each participant crawls different parts of the web. However, our sample size of 85,308 domains is significant. Our manual checks also validated that we would see similar results when we looked at the data that way.

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